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• semi
  semi

  noun

  semitrailer.
• semi-
  semi-

  a combining form borrowed from Latin, meaning “half,” freely prefixed to English words of any origin, now sometimes with the senses “partially,” “incompletely,” “somewhat”.
• semi–
  semi–

  A prefix that means “half,” (as in semicircle, half a circle) or “partly, somewhat, less than fully,” (as in semiconscious, partly conscious).

semi

¹ American  

[sem-ee, sem-ahy] / ˈsɛm i, ˈsɛm aɪ /

noun

Informal.

• semis
  plural

1. semitrailer.

2. Often semifinal.

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semi- ² American  

1. a combining form borrowed from Latin, meaning “half,” freely prefixed to English words of any origin, now sometimes with the senses “partially,” “incompletely,” “somewhat”.

   semiautomatic; semidetached; semimonthly; semisophisticated.

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semi ¹ British  

/ ˈsɛmɪ /

noun

1. a semidetached house

2. short for semifinal

3. short for semitrailer

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semi- ² British  

prefix

1. half Compare demi- hemi-

   semicircle

2. partially, partly, not completely, or almost

   semiprofessional

   semifinal

3. occurring twice in a specified period of time

   semiannual

   semiweekly

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semi– Scientific  

1. A prefix that means “half,” (as in semicircle, half a circle) or “partly, somewhat, less than fully,” (as in semiconscious, partly conscious).

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Usage

What does semi- mean? Semi- is a combining form used like a prefix meaning “half.” In some instances, it is used figuratively to mean "partially," "incompletely," or "somewhat." It is often used in a variety of technical and everyday terms. Semi- comes from Latin sēmi-, meaning “half.” The Greek cognate of sēmi- is hēmi-, also meaning “half,” which is the source of English terms such as hemialgia and hemicardia. To learn more, check out our entries for both words.

Commonly Confused

See bi- ¹.

Other Word Forms

Noun Inflected Forms

• semis
  plural

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Etymology

Origin of semi¹

By shortening

Origin of semi-²

Middle English < Latin sēmi-; cognate with Old English sōm-, sām- half (modern dial. sam- ), Old High German sāmi-, Sanskrit sāmi-, Greek hēmi-; cf. sesqui-

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Example Sentences

See Examples For:

semi semi- semi– semis

He also reached the semi finals of the World Cup with England.

From BBC ● Oct. 27, 2026

It had a semi debt crisis in the 1990s, when its debt-servicing costs climbed toward 10% of GDP.

From MarketWatch ● Sep. 29, 2026

Moderna stock surged following positive cancer-vaccine data, burning short sellers and spilling over into the semi sector.

From Barron's ● Aug. 21, 2026

On an earnings call, Elon Musk walked back earlier rollout guidance for Tesla’s Robotaxi service, Optimus robots and electric semi truck.

From The Wall Street Journal ● Jul. 23, 2026

When the third semi blew past us without even slowing down, Granny said, “I am only attending to your best interests.”

From "Louisiana's Way Home" by Kate DiCamillo

He “did not adopt a reflexive posture to protect himself and ... he may have fallen in a state of semi- or total unconsciousness,” officials said last month.

From Los Angeles Times ● Nov. 7, 2024

Semi-pedestal sinks are wall-hung sinks with a semi- or half-pedestal attached to the bottom of the sink.

From Seattle Times ● Feb. 28, 2022

Mr Stevenson, who died in 2004, had officiated at the semi- final of the 1979 tournament, and offered to take the child to the final.

From BBC ● Dec. 5, 2016

He's doubled it in a course of almost eight years, seven-and-a-half years, to be semi- exact.

From Washington Post ● Sep. 26, 2016

Besides, all the energy has flowed out to the new developments, to the semi- rural supermarkets, the outdoor movies, new houses with wide lawns and stucco schools where children are confirmed in their illiteracy.

From "Travels with Charley in Search of America" by John Steinbeck

Whole vase covered with thin semi– lustrous wash varying from red–brown to black.

From How to Observe in Archaeology by Various

“There was a lot of volatility for semis in the quarter,” he said.

From MarketWatch ● Oct. 27, 2026

“The semis have been so sensitive to the AI-infrastructure buildout,” Mike Reynolds, vice president of investment strategy at wealth-management firm Glenmede, said in a phone interview Friday.

From MarketWatch ● Oct. 23, 2026

He will play Gerwyn Price in the semis after the Welshman's superb 3-2 comeback success against his compatriot Jonny Clayton, who spurned a two-set lead and match darts in a thrilling tie.

From BBC ● Oct. 2, 2026

Powering aboard the 75-foot Mighty Mary, the women defeated the legendary Dennis Conner’s Stars & Stripes in the semis to book a spot in the final.

From The Wall Street Journal ● Oct. 2, 2026

I made it through the morning, but I was beaten in the semis and ended up in third place.

From "Ugly" by Robert Hoge

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