Definition of penicillin
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
Recent Examples of penicillin from the Web
Alexander Fleming [the biologist who serendipitously discovered penicillin] loved games.
This would not be too remarkable, except that since the 1970s, gonorrhea has become resistant first to penicillins, then to tetracycline, and then to fluoroquinolones (such as Cipro).
These example sentences are selected automatically from various online news sources to reflect current usage of the word 'penicillin'. Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.
Origin and Etymology of penicillin
New Latin Penicillium
First Known Use: 1929See Words from the same year
PENICILLIN Defined for English Language Learners
Definition of penicillin for English Language Learners
: a medicine that is used to kill harmful bacteria
PENICILLIN Defined for Kids
Definition of penicillin for Students
: an antibiotic that is produced by a mold and is used against disease-causing bacteria
Medical Definition of penicillin
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
Seen and Heard
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