penicillin
Americannoun
noun
-
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
Discover More
Penicillin was first widely used during World War II.
Other Word Forms
Noun Inflected Forms
Etymology
Origin of penicillin
First recorded in 1925–30; penicill(ium) + -in 2
Compare meaning
How does penicillin compare to similar and commonly confused words? Explore the most common comparisons:
Explanation
If you have an ear infection, your doctor may give you penicillin. It's a common kind of antibiotic medicine. Penicillin is credited with saving millions of lives. It was discovered in 1928 by a Scottish scientist who returned from a vacation to find a mold growing in a petri dish of infectious bacteria. There were no bacteria growing around the mold, and he named the antibacterial substance produced by the mold penicillin. About 10 years later, a team of different scientists started to figure out how to purify and mass-produce penicillin. The Latin root, penicillus, or "paintbrush," describes the shape of the mold cells that were used to create the original penicillin.
Vocabulary lists containing penicillin
List 10
Looking to grow your vocabulary? Check out this interactive, curated word list from our team of English language specialists at Vocabulary.com – one of over 17,000 lists we've built to help learners worldwide!
List 10
Interested in learning more words like this one? Our team at Vocabulary.com has got you covered! You can review flashcards, quiz yourself, practice spelling, and more – and it's all completely free to use!
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
One of those compounds was probenecid, a medication originally introduced in the 1940s to help conserve scarce supplies of penicillin by reducing how much of the antibiotic was excreted in urine.
From Science Daily ● Jun. 17, 2026
Alexander Fleming discovered penicillin after mould accidentally contaminated a laboratory dish and killed surrounding bacteria.
From Science Daily ● Mar. 14, 2026
Common problems that could have been treated with an office visit and a few penicillin pills will blossom into heart-valve infections and organ failure.
From MarketWatch ● Jan. 26, 2026
He has been raising concerns about production of everything from bombs to rare earths to penicillin, saying manufacturing is lagging behind and an investment plan is needed.
From The Wall Street Journal ● Dec. 8, 2025
The dim hospital corridor smelled of urine and penicillin.
From "Half of a Yellow Sun" by Chimamanda Ngozi Adichie
Some bacteria have developed the ability to break down beta-lactam antibiotics like penicillins and cephalosporins, making them ineffective.
From Science Daily ● Feb. 1, 2024
The second were synthetic penicillins, modified in the lab to resist the bugs' enzymes.
From The Guardian ● Jan. 24, 2013
Others, such as cephalosporins and penicillins, kill bacteria in a time-dependent fashion, based on the length of exposure to the drug.
From Scientific American ● Oct. 19, 2011
They are also closely related to the penicillins.
From BBC ● Jul. 11, 2011
By the middle of the century, Fleming's discovery had spawned a huge pharmaceutical industry, churning out synthetic penicillins that would conquer some of mankind's most ancient scourges, including syphilis, gangrene and tuberculosis.
From Time Magazine Archive
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
