An ordinal number or an ordinal is a word such as `first', `third', and `tenth' that tells you where a particular thing occurs in a sequence of things. Compare cardinal number. A number indicating position in a series or order. The ordinal numbers are first (1st), second (2nd), third (3rd), and so on. one of the numbers such as first, second, third etc which show the order of things cardinal number (ordinalis, from ordo; ORDER)