cardinal number

Noun

cardinal number (plural cardinal numbers)

1. A number used to denote quantity; a counting number; a cardinal.
   • The smallest cardinal numbers are 0, 1, 2, and 3.
   • The cardinal number “three” can be represented as “3” or “three”.

   Synonyms:

   cardinal, word

2. A generalized kind of number used to denote the size of a set, including infinite sets.
   • This cardinal number is the smallest of the infinite cardinal numbers; it is the one to which Cantor has appropriated the Hebrew Aleph with the suffix 0, to distinguish it from larger infinite cardinals. Thus the name of the smallest of infinite cardinals is ℵ₀.1920, Bertrand Russell, Introduction to Mathematical Philosophy, page 83
3. A word that expresses a countable quantity; a cardinal numeral.
   • “Three” is a cardinal number, while “third” is an ordinal number.