A cardinal number is a number such as 1, 3, or 10 that tells you how many things there are in a group but not what order they are in. Compare ordinal number. A number, such as 3 or 11 or 412, used in counting to indicate quantity but not order. a number such as 1, 2, or 3, that shows how many of something there are, but not what order they are in ordinal number