/ Dictionary / Index A ampicillin: Meaning and Definition of Find definitions for: am•pi•cil•lin Pronunciation: (am"pu-sil'in), [key] — n. Pharm. a broad-spectrum semisynthetic penicillin, CHNOS, effective against certain susceptible Gram-positive and Gram-negative bacteria. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: ampicillin (Thesaurus) amp-hr ample Related Content Daily Word Quiz: philtrum Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language