penicillin

noun

pen·​i·​cil·​lin ˌpe-nə-ˈsi-lən 

1

: any of several relatively nontoxic antibiotic acids of the general formula C₉H₁₁N₂O₄SR that are produced by molds (genus Penicillium and especially P. notatum or P. chrysogenum) or synthetically and are used especially against gram-positive cocci

also : a mixture of such acids

2

: a salt or ester of a penicillin or a mixture of such salts or esters

Examples of penicillin in a Sentence

Recent Examples on the Web

The vast majority of the prescriptions filled in the country are for generic drugs, from penicillin to blood thinners to emergency contraception, and many of those come from overseas, including India and China. —Debbie Cenziper, CNN Money, 20 June 2025

Penicillium molds produce the antibiotic penicillin, which has saved untold lives by warding off bacterial infection. —Cody Cottier, Discover Magazine, 5 May 2025

The scientists started with a molecule derived from the natural compound coumarin, and chemically linked it to the component of penicillin that kills bacteria by destroying their cell walls. —Ben Coxworth, New Atlas, 13 June 2025

Mark Cuban, whose Cost-Plus Drug Company manufactures and sells generic drugs, such as penicillin imported from Portugal, told Forbes that any costs elevated by tariffs will absolutely be passed through to patients. —Amy Feldman, Forbes.com, 9 Apr. 2025

Word History

Etymology

New Latin Penicillium

First Known Use

1929, in the meaning defined at sense 1

Rhymes for penicillin

• ampicillin
• methicillin
• pyroxylin
• amoxicillin
• carbenicillin
• haematoxylin
• millon
• villain
• vanillin

Kids Definition

penicillin

noun

pen·​i·​cil·​lin ˌpen-ə-ˈsil-ən 

: any of several antibiotics or a mixture of these produced by penicillia or in the laboratory and used especially against round disease-producing bacteria

Etymology

from scientific Latin Penicillium "a genus of molds producing antibiotics," from Latin penicillus, literally, "little tail" — related to pencil

Medical Definition

penicillin

noun

pen·​i·​cil·​lin ˌpen-ə-ˈsil-ən 

1

: a mixture of relatively nontoxic antibiotic acids produced especially by molds of the genus Penicillium (as P. notatum or P. chrysogenum) and having a powerful bacteriostatic effect against various chiefly gram-positive bacteria (as staphylococci, gonococci, pneumococci, hemolytic streptococci, or some meningococci)

2

: any of numerous often hygroscopic and unstable amido acids (as penicillin G, penicillin O, and penicillin V) that have a structure in which a four-membered lactam ring shares a nitrogen and a carbon atom with a thiazolidine ring to which it is fused and that are components of the penicillin mixture or are produced biosynthetically by the use of different strains of molds or different media or are synthesized chemically

3

: a salt or ester of a penicillin acid or a mixture of such salts or esters