penicillin

American  

[pen-uh-sil-in] / ˌpɛn əˈsɪl ɪn /

noun

Pharmacology.

penicillins plural

1. 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.

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penicillin British  

/ ˌpɛnɪˈsɪlɪn /

noun

1. 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-C 9 H 11 N 2 O 4 S where R is one of several side chains

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penicillin Scientific  

/ pĕn′ĭ-sĭl′ĭn /

1. 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.

2. See Note at Alexander Fleming

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penicillin Cultural  

1. 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.

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Discover More

Penicillin was first widely used during World War II.

Other Word Forms

Noun Inflected Forms

• penicillins
  plural

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:

• ampicillin vs. penicillin
• penicillin vs. amoxicillin

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.

Example Sentences

See Examples For:

penicillin penicillins

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

Lifeline follows the story of Sir Alexander Fleming's discovery of penicillin at St Mary's Hospital in Paddington in 1928, weaving his historical journey with a contemporary narrative centred on a junior doctor in Edinburgh.

From BBC ● Apr. 5, 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

She broke open one of the tiny penicillin bottles she often bought when she shopped at a pharmacy, and tried giving my brothers a penicillin injection.

From "Tasting the Sky" by Ibtisam Barakat

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

It steadily gained resistance against entire classes of antibiotics: first the penicillins in the 1960s, then the tetracyclines in the 1980s, and Cipro and its chemical cousins, known as fluoroquinolones, in the 1990s.

From Scientific American ● May 4, 2012

They are also closely related to the penicillins.

From BBC ● Jul. 11, 2011

Early penicillins were active mainly against the berry-shaped microbes or cocci, such as streptococci, staphylococci and pneumococci.

From Time Magazine Archive