penicillin

noun pen·i·cil·lin \ ˌpe-nə-ˈsi-lən \

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

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Recent Examples of penicillin from the Web

Although penicillin had become accepted as the cure by 1945, Tuskegee researchers left the men untreated until 1972, when the study was shut down.

— author: jan hoffman, Alaska Dispatch News, "Hunting a killer in Oklahoma: Sex, drugs and the return of syphilis," 25 Aug. 2017
Although penicillin had become accepted as the cure by 1945, Tuskegee researchers left the men untreated until 1972, when the study was shut down.

— author: jan hoffman, Alaska Dispatch News, "Hunting a killer in Oklahoma: Sex, drugs and the return of syphilis," 25 Aug. 2017
Although penicillin had become accepted as the cure by 1945, Tuskegee researchers left the men untreated until 1972, when the study was shut down.

— jan hoffman, The Seattle Times, "Once thought all but conquered, syphilis has come roaring back," 24 Aug. 2017
Unfortunately, many types of bacteria have grown resistant to penicillin: Staphylococcus Aureus, the bacteria commonly responsible for skin infections no longer responds to this class of antibiotics.

— maya wei-haas, Smithsonian, "This Is Why Taking Fish Medicine Is Truly a Bad Idea," 30 July 2017
Gonorrhea has already proven too resistant to other antibiotics, including penicillin, tetracycline, and ciprofloxacin.

— beth mole, Ars Technica, "Incurable gonorrhea is lurking—and we may not see it coming, WHO warns," 9 July 2017
White men discovered penicillin, Novocain, the drug regimen used to treat people afflicted with AIDS.

— ellen mcgirt, Fortune, "Five Breaking News Haikus," 7 July 2017
Gonorrhea has developed resistance to nearly every class of antibiotics used to treat it such as penicillin, tetracycline and fluoroquinolones, the CDC said.

— nicole chavez, CNN, "This STD is becoming 'smarter' and harder to treat," 7 July 2017
Of those, 100 children were tested for penicillin allergy using a standard, three-part testing process.

— maureen salamon, chicagotribune.com, "Lots of kids misdiagnosed as allergic to penicillin: Report," 7 July 2017

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

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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

Learn More about penicillin

Spanish Central: Translation of penicillin Nglish: Translation of penicillin for Spanish speakers Britannica.com: Encyclopedia article about penicillin

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