denominator

IPA/dɪˈnɒmɪneɪtə(r)/
KK[dɪnˈɑmənˌetɚ]IPA/dɪˈnɑːmɪneɪtər/

denominator — noun

  • denominatorsingular
  • denominatorsplural

1. In a written fraction, the figure placed below the horizontal dividing line that

1.nounB2
Definition

In a written fraction, the figure placed below the horizontal dividing line that indicates how many identical pieces the whole has been split into — for instance, the 4 in ¾ tells you the whole was divided into 4 equal portions.

Example

Nila forgot whether the denominator is the top or bottom number in a fraction.

basic concept: identifying numerator vs denominator

When Nia added ¼ and ⅜, she first checked whether they shared the same denominator.

collocation: share / same denominator

Common collocations
  • common denominator
  • least common denominator
  • same denominator
  • denominator of [number]
  • denominator cannot be zero
Synonyms
  • divisor

    more general term used in arithmetic; a divisor can appear outside fraction notation

  • bottom number

    informal, used mainly in primary-school math teaching

Antonyms
  • numerator

    the top number in a fraction, indicating how many parts are taken

Grammar Patterns

the denominator of [number]

Usage Note

Unlike the numerator, the denominator is never zero. Learners who are unsure which number in a fraction is the denominator can remember: it is the bottom figure, the one written below the horizontal bar.

Common Mistakes

The denominator is 3 in the fraction ⅓.
The denominator is 3 in the fraction ⅓
wait, that is actually correct.' (This is a trick — 3 is indeed the denominator in ⅓. A real mistake: ❌ 'The denominator is the top number.' ✅ 'The denominator is the bottom number; the top number is the numerator.' — The two terms are often confused.)
You can write a fraction with zero as the denominator.
The denominator can never be zero because dividing by zero has no meaning in mathematics.
Zero in the denominator makes the fraction undefined.

Word family

Synonym discussion

Sense: noun/1

Denominator refers specifically to the bottom figure in a fraction — it tells you how many equal pieces make up one whole (e.g., the 4 in ¾). Divisor is a broader arithmetic term: it means any number that divides another, whether or not it appears in a fraction, as in '12 ÷ 3 = 4, so 3 is the divisor.' Bottom number is an informal classroom label used to avoid the technical term 'denominator.' For example: 'The denominator of ¾ is 4' (precise math language); 'Divide 15 by 5 — 5 is the divisor' (general division); 'Write the bottom number under the line' (beginner instruction).

denominator ↗divisor ↗bottom number

Common collocations

Nouns

Phrases

  • common denominator
  • least common denominator
  • lowest common denominator

Prepositions

  • of [a fraction]
  • with [a common] denominator

Etymology

LatinFrenchEnglish

From late Latin 'denominātor' (that which names), formed from 'dē-' (down, away) + 'nōmināre' (to name). In medieval mathematics, the denominator was understood as 'the number that names the parts' — e.g., 'fourths' in ¾, 'fifths' in ⅖. The word entered English mathematical writing in the 1500s through Latin-influenced textbooks.