ordinal numberordinal number
any number used to indicate order (e.g., second, ninth, 25th) in a particular series
A number indicating position in a series or order. The ordinal numbers are first (1st), second (2nd), third (3rd), and so on.
(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 a3, the "3" is an ordinal number.
- (mathematics) A generalized kind of number to denote the length of a well-order on a set.
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.
- attributive form of ordinal number, noun.