/ Dictionary / Index A aleph-null: Meaning and Definition of Find definitions for: a•leph-null Pronunciation: (ä'lif-nul'), [key] — n. Math. the cardinal number of the set of all positive integers; the smallest transfinite cardinal number. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: aleph-null (Thesaurus) aleph Aleppo Related Content Daily Word Quiz: winsome Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language