¦ampə¦silə̇n noun
( -s )
Etymology: am in- + p en icillin
: a penicillin C 16 H 19 N 3 O 4 S that is effective against gram-negative and gram-positive bacteria and is used in anhydrous forms, as the trihydrate, or as the sodium salt to treat various infections of the urinary, respiratory, and intestinal tracts