diff --git a/README.md b/README.md
index 658a891..b969f84 100644
--- a/README.md
+++ b/README.md
@@ -23,7 +23,7 @@ const hexDigit = charClass(
 
 const hexColor = buildRegExp(
   startOfString,
-  optionally('#'),
+  optional('#'),
   capture(
     choiceOf(
       repeat(hexDigit, 6), // #rrggbb
@@ -85,7 +85,7 @@ const currencyAmount = buildRegExp([
   ),
   capture(
     oneOrMore(digit), // Integer part
-    optionally(['.', repeat(digit, 2)]), // Fractional part
+    optional(['.', repeat(digit, 2)]), // Fractional part
   ),
 ]);
 ```
@@ -112,7 +112,7 @@ Comprehensive API document is available [here](./API.md).
 | -------------------------------- | ------------- | ------------------------------------------------- |
 | `zeroOrMore(x)`                  | `x*`          | Zero or more occurence of a pattern               |
 | `oneOrMore(x)`                   | `x+`          | One or more occurence of a pattern                |
-| `optionally(x)`                  | `x?`          | Zero or one occurence of a pattern                |
+| `optional(x)`                    | `x?`          | Zero or one occurence of a pattern                |
 | `repeat(x, n)`                   | `x{n}`        | Pattern repeats exact number of times             |
 | `repeat(x, { min: n, })`         | `x{n,}`       | Pattern repeats at least given number of times    |
 | `repeat(x, { min: n, max: n2 })` | `x{n1,n2}`    | Pattern repeats between n1 and n2 number of times |
diff --git a/docs/API.md b/docs/API.md
index 70e4e2a..88dbd8d 100644
--- a/docs/API.md
+++ b/docs/API.md
@@ -100,17 +100,17 @@ Regex syntax: `x+`;
 
 The `oneOrMore` quantifier matches one or more occurrences of given pattern, allowing a flexible number of repetitions of that element.
 
-### `optionally()`
+### `optional()`
 
 ```ts
-function optionally(
+function optional(
   sequence: RegexSequence,
 ): Optionally
 ```
 
 Regex syntax: `x?`;
 
-The `optionally` quantifier matches zero or one occurrence of given pattern, making it optional.
+The `optional` quantifier matches zero or one occurrence of given pattern, making it optional.
 
 ### `repeat()`
 
diff --git a/docs/Examples.md b/docs/Examples.md
index 10c891a..bd96a87 100644
--- a/docs/Examples.md
+++ b/docs/Examples.md
@@ -3,16 +3,16 @@
 ## JavaScript number
 
 ```ts
-const optionalSign = optionally(anyOf('+-'));
-const exponent = [anyOf('eE'), optionalSign, oneOrMore(digit)];
+const sign = anyOf('+-');
+const exponent = [anyOf('eE'), optional(sign), oneOrMore(digit)];
 
 const regex = buildRegExp([
-  optionalSign,
+  optional(sing),
   choiceOf(
-    [oneOrMore(digit), optionally(['.', zeroOrMore(digit)])], // leading digit
+    [oneOrMore(digit), optional(['.', zeroOrMore(digit)])], // leading digit
     ['.', oneOrMore(digit)], // leading dot
   ),
-  optionally(exponent), // exponent
+  optional(exponent), // exponent
 ]);
 ```
 
diff --git a/src/__tests__/examples.test.ts b/src/__tests__/examples.test.ts
index 0155b4d..6455069 100644
--- a/src/__tests__/examples.test.ts
+++ b/src/__tests__/examples.test.ts
@@ -6,24 +6,24 @@ import {
   digit,
   endOfString,
   oneOrMore,
-  optionally,
+  optional,
   repeat,
   startOfString,
   zeroOrMore,
 } from '../index';
 
 test('example: validate JavaScript number', () => {
-  const optionalSign = optionally(anyOf('+-'));
-  const exponent = [anyOf('eE'), optionalSign, oneOrMore(digit)];
+  const sign = anyOf('+-');
+  const exponent = [anyOf('eE'), optional(sign), oneOrMore(digit)];
 
   const regex = buildRegExp([
     startOfString,
-    optionalSign,
+    optional(sign),
     choiceOf(
-      [oneOrMore(digit), optionally(['.', zeroOrMore(digit)])], // leading digit
+      [oneOrMore(digit), optional(['.', zeroOrMore(digit)])], // leading digit
       ['.', oneOrMore(digit)], // leading dot
     ),
-    optionally(exponent), // exponent
+    optional(exponent), // exponent
     endOfString,
   ]);
 
diff --git a/src/constructs/__tests__/character-class.test.ts b/src/constructs/__tests__/character-class.test.ts
index 7a60c4d..bc8d703 100644
--- a/src/constructs/__tests__/character-class.test.ts
+++ b/src/constructs/__tests__/character-class.test.ts
@@ -1,4 +1,4 @@
-import { oneOrMore, optionally, zeroOrMore } from '../quantifiers';
+import { oneOrMore, optional, zeroOrMore } from '../quantifiers';
 import {
   any,
   anyOf,
@@ -76,7 +76,7 @@ test('`anyOf` base cases', () => {
 
 test('`anyOf` with quantifiers', () => {
   expect(['x', oneOrMore(anyOf('abc')), 'x']).toHavePattern(/x[abc]+x/);
-  expect(['x', optionally(anyOf('abc')), 'x']).toHavePattern(/x[abc]?x/);
+  expect(['x', optional(anyOf('abc')), 'x']).toHavePattern(/x[abc]?x/);
   expect(['x', zeroOrMore(anyOf('abc')), 'x']).toHavePattern(/x[abc]*x/);
 });
 
diff --git a/src/constructs/__tests__/quantifiers.test.tsx b/src/constructs/__tests__/quantifiers.test.tsx
index 22a2584..cb882c0 100644
--- a/src/constructs/__tests__/quantifiers.test.tsx
+++ b/src/constructs/__tests__/quantifiers.test.tsx
@@ -1,14 +1,14 @@
 import { digit } from '../character-class';
-import { oneOrMore, optionally, zeroOrMore } from '../quantifiers';
+import { oneOrMore, optional, zeroOrMore } from '../quantifiers';
 
 test('`oneOrMore` quantifier', () => {
   expect(oneOrMore('a')).toHavePattern(/a+/);
   expect(oneOrMore('ab')).toHavePattern(/(?:ab)+/);
 });
 
-test('`optionally` quantifier', () => {
-  expect(optionally('a')).toHavePattern(/a?/);
-  expect(optionally('ab')).toHavePattern(/(?:ab)?/);
+test('`optional` quantifier', () => {
+  expect(optional('a')).toHavePattern(/a?/);
+  expect(optional('ab')).toHavePattern(/(?:ab)?/);
 });
 
 test('`zeroOrMore` quantifier', () => {
@@ -20,8 +20,8 @@ test('`oneOrMore` does not generate capture when grouping', () => {
   expect(oneOrMore('aa')).toMatchGroups('aa', ['aa']);
 });
 
-test('`optionally` does not generate capture when grouping', () => {
-  expect(optionally('aa')).toMatchGroups('aa', ['aa']);
+test('`optional` does not generate capture when grouping', () => {
+  expect(optional('aa')).toMatchGroups('aa', ['aa']);
 });
 
 test('`zeroOrMore` does not generate capture when grouping', () => {
@@ -30,10 +30,10 @@ test('`zeroOrMore` does not generate capture when grouping', () => {
 
 test('base quantifiers optimize grouping for atoms', () => {
   expect(oneOrMore(digit)).toHavePattern(/\d+/);
-  expect(optionally(digit)).toHavePattern(/\d?/);
+  expect(optional(digit)).toHavePattern(/\d?/);
   expect(zeroOrMore(digit)).toHavePattern(/\d*/);
 
   expect(oneOrMore('a')).toHavePattern(/a+/);
-  expect(optionally('a')).toHavePattern(/a?/);
+  expect(optional('a')).toHavePattern(/a?/);
   expect(zeroOrMore('a')).toHavePattern(/a*/);
 });
diff --git a/src/constructs/quantifiers.ts b/src/constructs/quantifiers.ts
index c96a71d..77bb165 100644
--- a/src/constructs/quantifiers.ts
+++ b/src/constructs/quantifiers.ts
@@ -3,19 +3,27 @@ import type { EncodeResult } from '../encoder/types';
 import { ensureArray } from '../utils/elements';
 import type { RegexConstruct, RegexElement, RegexSequence } from '../types';
 
+export interface ZeroOrMore extends RegexConstruct {
+  type: 'zeroOrMore';
+  children: RegexElement[];
+}
+
 export interface OneOrMore extends RegexConstruct {
   type: 'oneOrMore';
   children: RegexElement[];
 }
 
-export interface Optionally extends RegexConstruct {
-  type: 'optionally';
+export interface Optional extends RegexConstruct {
+  type: 'optional';
   children: RegexElement[];
 }
 
-export interface ZeroOrMore extends RegexConstruct {
-  type: 'zeroOrMore';
-  children: RegexElement[];
+export function zeroOrMore(sequence: RegexSequence): ZeroOrMore {
+  return {
+    type: 'zeroOrMore',
+    children: ensureArray(sequence),
+    encode: encodeZeroOrMore,
+  };
 }
 
 export function oneOrMore(sequence: RegexSequence): OneOrMore {
@@ -26,19 +34,18 @@ export function oneOrMore(sequence: RegexSequence): OneOrMore {
   };
 }
 
-export function optionally(sequence: RegexSequence): Optionally {
+export function optional(sequence: RegexSequence): Optional {
   return {
-    type: 'optionally',
+    type: 'optional',
     children: ensureArray(sequence),
-    encode: encodeOptionally,
+    encode: encodeOptional,
   };
 }
 
-export function zeroOrMore(sequence: RegexSequence): ZeroOrMore {
+function encodeZeroOrMore(this: ZeroOrMore): EncodeResult {
   return {
-    type: 'zeroOrMore',
-    children: ensureArray(sequence),
-    encode: encodeZeroOrMore,
+    precedence: 'sequence',
+    pattern: `${encodeAtom(this.children).pattern}*`,
   };
 }
 
@@ -49,16 +56,9 @@ function encodeOneOrMore(this: OneOrMore): EncodeResult {
   };
 }
 
-function encodeOptionally(this: Optionally): EncodeResult {
+function encodeOptional(this: Optional): EncodeResult {
   return {
     precedence: 'sequence',
     pattern: `${encodeAtom(this.children).pattern}?`,
   };
 }
-
-function encodeZeroOrMore(this: ZeroOrMore): EncodeResult {
-  return {
-    precedence: 'sequence',
-    pattern: `${encodeAtom(this.children).pattern}*`,
-  };
-}
diff --git a/src/encoder/__tests__/encoder.test.tsx b/src/encoder/__tests__/encoder.test.tsx
index d52dc3f..86f9ce2 100644
--- a/src/encoder/__tests__/encoder.test.tsx
+++ b/src/encoder/__tests__/encoder.test.tsx
@@ -1,5 +1,5 @@
 import { buildPattern, buildRegExp } from '../../builders';
-import { oneOrMore, optionally, zeroOrMore } from '../../constructs/quantifiers';
+import { oneOrMore, optional, zeroOrMore } from '../../constructs/quantifiers';
 import { repeat } from '../../constructs/repeat';
 
 test('basic quantifies', () => {
@@ -7,7 +7,7 @@ test('basic quantifies', () => {
   expect(['a', 'b']).toHavePattern(/ab/);
 
   expect(oneOrMore('a')).toHavePattern(/a+/);
-  expect(optionally('a')).toHavePattern(/a?/);
+  expect(optional('a')).toHavePattern(/a?/);
 
   expect(['a', oneOrMore('b')]).toHavePattern(/ab+/);
   expect(['a', oneOrMore('bc')]).toHavePattern(/a(?:bc)+/);
@@ -19,9 +19,9 @@ test('basic quantifies', () => {
   expect(['a', zeroOrMore('bc')]).toHavePattern(/a(?:bc)*/);
   expect(['a', zeroOrMore('bc')]).toHavePattern(/a(?:bc)*/);
 
-  expect([optionally('a'), 'b']).toHavePattern(/a?b/);
+  expect([optional('a'), 'b']).toHavePattern(/a?b/);
 
-  expect([optionally('a'), 'b', oneOrMore('d')]).toHavePattern(/a?bd+/);
+  expect([optional('a'), 'b', oneOrMore('d')]).toHavePattern(/a?bd+/);
 });
 
 test('`buildPattern` escapes special characters', () => {
diff --git a/src/index.ts b/src/index.ts
index 9bfb3d5..d7f7514 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -15,5 +15,5 @@ export {
   inverted,
 } from './constructs/character-class';
 export { choiceOf } from './constructs/choice-of';
-export { oneOrMore, optionally, zeroOrMore } from './constructs/quantifiers';
+export { oneOrMore, optional, zeroOrMore } from './constructs/quantifiers';
 export { repeat } from './constructs/repeat';