penicillin

noun pen·i·cil·lin \ ˌpe-nə-ˈsi-lən \

Updated on: 24 Apr 2018

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

See penicillin defined for English-language learners

See penicillin defined for kids

Recent Examples of penicillin from the Web

Patrice Comey launched a campaign to require doctors and hospitals to test for Group B streptococcus, a bacterial infection that can be treated with penicillin during delivery if detected toward the end of a pregnancy.

— susan page, USA TODAY, "James Comey: Lessons he learned from the tragic loss of his infant son," 16 Apr. 2018
Notes: Data is as of 2013; penicillin was in limited use prior to widespread population usage in 1943.

— betsy mckay, WSJ, "Rare Superbugs More Widespread Than Thought, Says CDC," 3 Apr. 2018
If caught early, syphilis is easily treated with penicillin.

— matthew ormseth, courant.com, "Hartford Secures Grant To Combat Syphilis, On The Rebound In Connecticut And The Country," 6 Apr. 2018
Antibiotics have been a critical public health tool since the discovery of penicillin in 1928, saving the lives of millions of people around the world.

— lisa m. krieger, chicagotribune.com, "'A last line of defense': IBM lab designs molecule to kill drug-resistant superbugs," 4 Apr. 2018
Notes: Data is as of 2013; penicillin was in limited use prior to widespread population usage in 1943.

— betsy mckay, WSJ, "Rare Superbugs More Widespread Than Thought, Says CDC," 3 Apr. 2018
The use of broad-spectrum penicillins—the most common type of antibiotics—increased by 36%.

— Time, "People Around the World Are Using Far More Antibiotics," 26 Mar. 2018
The bacteria involved are resistant to not only methicillin but also amoxicillin, penicillin and oxycillin.

— cathie anderson, sacbee, "Influenza B surging as overall flu cases fall — and it's deadlier in kids, experts say | The Sacramento Bee," 19 Mar. 2018
Everyone loves the story of penicillin: One day, pharmacologist Alexander Fleming returned from a two-week vacation to Scotland, only to peer into a moldy Petri dish and find the world’s first antibiotic.

— brian handwerk, Smithsonian, "Sometimes, a Scientific “Eureka!” Moment Really Does Change The World," 7 Mar. 2018

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

NEW! Time Traveler

First Known Use: 1929

in the meaning defined at sense 1

See Words from the same year

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PENICILLIN Defined for English Language Learners

penicillin

noun

Definition of penicillin for English Language Learners

: a medicine that is used to kill harmful bacteria

PENICILLIN Defined for Kids

penicillin

noun pen·i·cil·lin \ ˌpe-nə-ˈsi-lən \

Definition of penicillin for Students

: an antibiotic that is produced by a mold and is used against disease-causing bacteria

Medical Dictionary

penicillin

noun pen·i·cil·lin \ ˌpen-ə-ˈsil-ən \

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