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

That could hurt consumers who rely on those low-cost alternatives to brand-name drugs for everything from antibiotics like penicillin to blood pressure medication. —Alex Knapp, Forbes.com, 8 Apr. 2025

And then there’s penicillin, one of the most important medical advances in history. —Ann Kowal Smith, Forbes, 21 Mar. 2025

Iron may also interact with certain antibiotics, including penicillin, tetracycline, and ciprofloxacin.1 These medications should be taken at least two hours apart from iron to avoid interactions. —Melissa Nieves, Verywell Health, 9 Jan. 2025

In the span of a few years, the agency spurred development of an antimalarial drug, a flu vaccine, techniques to produce penicillin at scale, and, less salubriously, the atomic bomb. —Dhruv Khullar, The New Yorker, 9 Mar. 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