fifteenth

fifteenth — adjective

1. coming or happening after the fourteenth in a numbered sequence — for example, t

1.adjectiveA1
Definition

coming or happening after the fourteenth in a numbered sequence — for example, the fifteenth day of a month, the fifteenth chapter of a book, or a fifteenth birthday party. This word is the ordinal form of the number fifteen.

Example

Evelyn's fifteenth birthday party will be held at the community centre this Saturday.

ordinal with possessive + noun (birthday)

The fifteenth chapter of the novel includes a surprising twist about the main character.

Common collocations
  • fifteenth birthday
  • fifteenth century
  • fifteenth floor
  • fifteenth chapter
  • fifteenth anniversary
  • fifteenth of [month]

Grammar Patterns

the fifteenth + noun

possessive + fifteenth + noun

Usage Note

When giving a date, 'fifteenth' is used after the name of the month: 'the fifteenth of May' or 'May fifteenth'. In American English, the shorter form 'May fifteenth' is more common, while British English more frequently uses 'the fifteenth of May'. This sense is the source of the numeral form '15th' used in informal writing.

Common Mistakes

I live on the fifteen floor.
I live on the fifteenth floor.
Ordinal numbers (first, second, third, fifteenth) must be used, not cardinal numbers (one, two, three, fifteen), when stating position in a series.
She came fifteen in the race.
She came fifteenth in the race.
'Fifteenth' (not 'fifteen') is the ordinal form needed for ranking and position.

2. accounting for one of the fifteen equal parts that a whole can be divided into —

2.adjectiveB1
Definition

accounting for one of the fifteen equal parts that a whole can be divided into — for example, a fifteenth share of a company's profits or a fifteenth portion of the total land area.

Example

Each of the fifteen partners received a fifteenth share of the company's yearly profit.

fractional adjective: a fifteenth share of + noun

A fifteenth portion of the inheritance was set aside for the youngest grandchild.

Common collocations
  • fifteenth share
  • fifteenth portion

Grammar Patterns

a fifteenth + noun

a fifteenth of + noun phrase

Usage Note

This fractional sense is less common than the ordinal sense (sense 1). It appears mainly in mathematical, financial, or measurement contexts. For everyday fractions of food or objects, speakers are more likely to say 'one fifteenth of the…' than use 'fifteenth' as a standalone adjective before the noun.

fifteenth — noun

Word family

Synonym discussion

Sense: adjective/1

The ordinal 'fifteenth' (15th) is often confused with the cardinal 'fifteen' (15) by learners. 'Fifteenth' always indicates position in a sequence, while 'fifteen' is a simple quantity. For example, a learner might say 'Chapter fifteen' (cardinal, the chapter labelled 15) versus 'the fifteenth chapter' (ordinal, the 15th chapter in order). Although both can refer to the same chapter in practice, the grammar differs: cardinal numbers follow the noun (Chapter fifteen) while ordinals precede it with 'the' (the fifteenth chapter). The similar-sounding 'five' and 'fifty' share sounds with 'fifteenth' ('fif-' and '-teen') but belong to entirely different number families. A concrete example: 'There are fifteen people in the room, and Evelyn is the fifteenth to speak.'

fifteenth ↗fifteen ↗five ↗fifty ↗

Common collocations

Phrases

  • the fifteenth of
  • on the fifteenth of
  • by the fifteenth of

Prepositions

  • on the fifteenth
  • of the fifteenth
  • by the fifteenth
  • until the fifteenth

Etymology

Old EnglishMiddle EnglishEnglish

The word 'fifteenth' comes from Old English 'fīfteōða', which meant 'fifth-teen' — a combination of 'fīf' (five) and 'tēona' (ten), reflecting that fifteen is five plus ten. The '-teenth' ending (as in 'thirteenth', 'fourteenth', 'sixteenth') evolved from Old English '-teoða', a suffix used to form ordinal numbers from the teens (13-19). By Middle English, it had become 'fiftenþe', and by the 1500s the modern spelling 'fifteenth' was standardised. The structure is parallel across all English ordinals from 13th to 19th: the cardinal number (thir-, four-, fif-, six-, etc.) plus the ordinal suffix '-teenth'.