# ordinal number

ordinal number any number used to indicate order (e.g., second, ninth, 25th) in a particular series

## ordinal number

noun

A number indicating position in a series or order. The ordinal numbers are first (1st), second (2nd), third (3rd), and so on.

## ordinal-number

Noun

(*plural* ordinal numbers)

- (grammar) A word that expresses the relative position of an item in an ordered sequence.
*First, second and third are the ordinal numbers corresponding to one, two and three.*

- (arithmetic) A number used to denote position in a sequence.
*In the expression a*_{3}, the "3" is an ordinal number.

- (mathematics) A generalized kind of number to denote the length of a well-order on a set.

Usage notes

On ordinal number usage:

- Ordinal numbers are generally construed as
*adjectives*preceding (countable) nouns in singular:*eleventh day*

- Ordinal numbers are used for fractions as (countable) nouns, and for exponents usually followed by
*power*and that numeral:*two fifths*,*two to the minus twenty-first power*,*six to the third*,

- Ordinal numbers are generally considered to be ordered from
*high*to*low*, so that*first place*is considered*highest*, and*fifth*is lower than*second*.*Degree*is an exception. - Ordinal numbers corresponding to numbers higher than 20 use cardinal numbers for all the places preceding the final ordinal part:
*twenty-first*or*21st*, occasionally*XXI**one hundred fifteenth*or*115th*, occasionally*CXV**thirty-three thousandth*or*33,000th*

- If an ordinal is followed by a plural noun, the two word phrase refers to a set of items described by the phrase in singular. For example
*second homes*refers to a set of homes which are considered a "second home."*Many households have*third*cars.*

Adjective

ordinal-number

- attributive form of
*ordinal number*,*noun*.

## ordinal number - Computer Definition

The number that identifies the sequence of an item, for example, record #34. Contrast with cardinal number.