1. Also called car'dinal nu'meral. any of the numbers that express amount, as one, two, three, etc. (distinguished from ordinal number).
2. Also called potency, power. Math.a number or symbol analogous to the number of elements in a finite set, being identical for two sets that can be placed into one-to-one correspondence: The cardinal number of the set a 1, a2, … an is n.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.