/ Dictionary / Index C CD4: Meaning and Definition of Find definitions for: CD4 Pronunciation: [key] a protein on the surface of T cells and other cells, functioning as a receptor for the AIDS virus antigen. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: cd4 (Thesaurus) CDC CD-I Related Content Daily Word Quiz: tenacious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language