gam·​ma | \ˈga-mə \

Definition of gamma 

(Entry 1 of 2)

1 : the 3rd letter of the Greek alphabet — see Alphabet Table

2 : the degree of contrast of a developed photographic image or of a video image

3 : a unit of magnetic flux density equal to one nanotesla

4 : gamma ray gamma counter

5 : microgram



Definition of gamma (Entry 2 of 2)

1 : of, relating to, or being one of three or more closely related chemical substances

2 : third in position in the structure of an organic molecule from a particular group or atom symbol γ

Examples of gamma in a Sentence

Recent Examples on the Web: Noun

Even more exciting, the bright gamma-ray glow fit quite well to dark matter being annihilated into a pair of matter/antimatter quarks. Chris Lee, Ars Technica, "Gamma ray evidence for dark matter outshone by a flock of pulsars," 10 Aug. 2018 Some of that atmospheric radiation makes its way into wine bottles, where it can be measured with a common gamma detector. Avery Thompson, Popular Mechanics, "Traces of the Fukushima Meltdown Can Be Found in California Wines," 21 July 2018 The $690 million spacecraft launched from Florida's Cape Canaveral Air Force Station on June 11, 2008, on a mission to study gamma-rays, the highest-energy form of light in the universe. Hanneke Weitering,, "NASA's Fermi Space Telescope Celebrates 10 Years of Gamma-Ray Science," 13 June 2018 Tanaka also works on the Fermi Gamma-ray Space Telescope, which has been taking images of the entire gamma-ray sky every three hours for about 10 years. Mark Bowen, Scientific American, "Neutrinos on Ice: Astronomers' Long Hunt for Source of Extragalactic "Ghost Particles" Pays Off," 12 July 2018 Six days after Tanaka’s alert, the operators of MAGIC, the Major Atmospheric Gamma Imaging Cherenkov Telescope on the La Palma Canary Island, announced the observation of very high-energy gammas coming from TXS. Mark Bowen, Scientific American, "Neutrinos on Ice: Astronomers' Long Hunt for Source of Extragalactic "Ghost Particles" Pays Off," 12 July 2018 When that happened, observatories around the world, from an optical telescope in the Canary Islands to a gamma-ray observatory orbiting hundreds of miles above the Earth, leapt to action. Eoin O'carroll, The Christian Science Monitor, "Neutrino demonstration heralds a new way of observing the cosmos," 12 July 2018 The community responded: Nearly 20 telescopes on the ground and in space scoured that patch across the electromagnetic spectrum, from low-energy radio waves to high-energy gamma-rays. Mike Wall, NBC News, "High-energy 'ghost particle' traced to distant galaxy in astronomy breakthrough," 12 July 2018 According to the study, in the 1970s, co-author Brazilian scientist Sérgio Mascarenhas discovered that X-Ray and gamma-ray radiation exposure caused human bones to become weakly magnetic. Julissa Treviño, Smithsonian, "Researchers Identify How Much Radiation Hiroshima Victims Were Exposed to," 3 May 2018

Recent Examples on the Web: Adjective

That spacecraft traced the neutrino back to an obscure dot in the sky, a distant galaxy known as TXS 0506+056, just off the left shoulder of the constellation Orion, which was having a high-energy outburst of X-rays and gamma-rays. Dennis Overbye, New York Times, "It Came From a Black Hole, and Landed in Antarctica," 12 July 2018 This revealed phytanic acid (frequently found in the fat and milk of ruminants), azelaic acid (common in wholegrain cereals) and gamma-terpinene (typically found in herbs like coriander). The Economist, "A mummy’s final meal adds to an ancient mystery," 12 July 2018 Of course the frisker was measuring gamma waves in addition to alpha and beta particles; all these people presumably cared about was the particles, which could continue to do harm after being removed from the zone. Aaron Gilbreath, Longreads, "As Innocuous as Plant No. 1," 10 Apr. 2018 Sony also adds support for gamma curves, allowing you to correct for different lighting situations while filming and ultimately, a different style for every curve. Stefan Etienne, The Verge, "Sony A7 III and A7R III review: mirrorless magic," 30 Mar. 2018 But black holes produce their own radiation, especially high-energy X-rays and gamma-rays, which shoot out from the star in the form of tightly collimated... Newsweek, "Analysis," 14 Mar. 2018 The collective radiation from all of these hydrogen atom collisions, in the form of light, heat, gamma rays, and X-rays, slowly makes its way to the outer layer of a star. Mike Lynch / Sky Watch, Twin Cities, "Sky Watch: Inside the violent core of a star (and our sun)," 18 Mar. 2017 The machine uses gamma rays to shrink brain tumors as an alternative to open-skull surgery, Andy Marso reports. Max Londberg,, "Morning Rush: Chiefs fire GM John Dorsey, roaches at area food operations, Big Slick," 23 June 2017 World View has since carried other experiments, including a gamma ray detector and a remote-sensing system. Adam Mann, Science | AAAS, "Commercial balloons in the stratosphere could monitor hurricanes and scan for solar storms," 22 June 2017

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'gamma.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

See More

First Known Use of gamma


15th century, in the meaning defined at sense 1


1834, in the meaning defined at sense 1

History and Etymology for gamma


Middle English, borrowed from Latin, borrowed from Greek gȧmma, borrowed from Phoenician *gaml-, perhaps with the original sense "throwing stick"


attributive use of gamma entry 1

Keep scrolling for more

Learn More about gamma

Statistics for gamma

Last Updated

20 Nov 2018

Look-up Popularity

Time Traveler for gamma

The first known use of gamma was in the 15th century

See more words from the same century

Keep scrolling for more

More Definitions for gamma



English Language Learners Definition of gamma

: the third letter of the Greek alphabet


gam·​ma | \ˈgam-ə \

Medical Definition of gamma 

(Entry 1 of 2)

1 : the third letter of the Greek alphabet symbol Γ or γ

2 : a unit of magnetic flux density equal to one nanotesla

3 : gamma ray usually used as the attributive form of gamma ray gamma counter


variants: or γ-

Medical Definition of gamma (Entry 2 of 2)

1 : of or relating to one of three or more closely related chemical substances the gamma chain of hemoglobin γ-yohimbine used somewhat arbitrarily to specify ordinal relationship or a particular physical form and especially one that is allotropic, isomeric, or stereoisomeric (as in gamma benzene hexachloride)

2 : third in position in the structure of an organic molecule from a particular group or atom also : occurring at or having a structure characterized by such a position γ-hydroxy acids

3 of streptococci : producing no hemolysis on blood agar plates

More from Merriam-Webster on gamma

Rhyming Dictionary: Words that rhyme with gamma Encyclopedia article about gamma

Comments on gamma

What made you want to look up gamma? Please tell us where you read or heard it (including the quote, if possible).


to enclose within walls

Get Word of the Day daily email!

Test Your Vocabulary

Late Autumn 2018 Words of the Day Quiz

  • frosted-autumn-leaves
  • Which is a synonym of yahoo?
True or False

Test your knowledge - and maybe learn something along the way.

Dictionary Devil

Test Your Knowledge - and learn some interesting things along the way.


Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!