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[pen-uh-sil-in] /ˌpɛn əˈsɪl ɪn/
noun, Pharmacology
any of several antibiotics of low toxicity, produced naturally by molds of the genus Penicillium and also semisynthetically, having a bactericidal action on many susceptible Gram-positive or Gram-negative cocci and bacilli, some also being effective against certain spirochetes.
1925-30; penicill(ium) + -in2 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for penicillin
  • And you are right that they lack the critical training to tell penicillin from snake oil.
  • penicillin is so good at killing bacteria that bacteria have had to evolve a way around it.
  • He chose one that he thought, at this point, would be even more effective than penicillin.
  • Even bacteria completely immune to penicillin and its cousins could be killed.
  • Her husband was taking penicillin for an ear infection, she added, but she'd had no direct contact with the medication.
  • The envelopes were taped shut, and the letters told people to take penicillin.
  • She was first deliberately infected with syphilis and, months later, given penicillin.
  • The test tubes in which the viruses are cultured contain penicillin to prevent bacterial spoilage.
  • The stated aim of the study was to see if penicillin could prevent infection after exposure.
  • The tablets are ampicillin, a common prescription antibiotic similar to penicillin.
British Dictionary definitions for penicillin


any of a group of antibiotics with powerful bactericidal action, used to treat many types of infections, including pneumonia, gonorrhoea, and infections caused by streptococci and staphylococci: originally obtained from the fungus Penicillium, esp P. notatum. Formula: R-C9H11N2O4S where R is one of several side chains
Word Origin
C20: from penicillium
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for penicillin

1929, coined in English by Alexander Fleming (1881-1955), who first recognized its antibiotic properties, from Modern Latin Penicillium notatum (1867), the name of the mould from which it was first obtained, from Latin penicillus "paintbrush" (see pencil (n.)), in reference to the shape of the mould cells.

Online Etymology Dictionary, © 2010 Douglas Harper
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penicillin in Medicine

penicillin pen·i·cil·lin (pěn'ĭ-sĭl'ĭn)
Any of a group of broad-spectrum antibiotic drugs obtained from penicillium molds or produced synthetically, most active against gram-positive bacteria and used in the treatment of various infections and diseases.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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penicillin in Science
An antibiotic drug obtained from molds of the genus Penicillium and used to treat or prevent various infections caused by gram-positive bacteria such as streptococcus. Penicillin was the first of a class of antibiotics (whose names end in -icillin) that are derived from it and are active against a broader spectrum of bacteria. See Note at Alexander Fleming.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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penicillin in Culture

penicillin definition

An antibiotic that is used to treat infections caused by some kinds of bacteria. Penicillin, which is derived from a common kind of mold that grows on bread and fruit, was the first antibiotic discovered and put into widespread use.

Note: Penicillin was first widely used during World War II.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Slang definitions & phrases for penicillin


Related Terms

jewish penicillin

The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D.
Copyright (C) 2007 by HarperCollins Publishers.
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