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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  

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 ² British  

/ ˈsɛmɪ /

noun

1. a semidetached house

2. short for semifinal

3. short for semitrailer

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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

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-

Example Sentences

See Examples For:

semi semi- semi– semis

A spot in the semi finals is on the line.

From BBC ● Jul. 11, 2026

The brothers were born in India and raised in Australia, where Johnny enjoyed a brief career as a semi professional cricket player.

From Los Angeles Times ● Jul. 3, 2026

“Some investors may be concluding that Mr. Durn’s departure for a semi company is an indication of that sector having a greater opportunity,” D.A.

From MarketWatch ● Jun. 12, 2026

And on its way to the final, the club averaged 2.75 goals per game, even putting five past Bayern Munich in the first leg of their semi.

From The Wall Street Journal ● May 30, 2026

Tomás stopped the semi in front of a chain-link gate.

From "Storm Runners" by Roland Smith

Curtis broke Australian Kaylee McKeown's previous record by 0.23 seconds with a time of 26.63s in the semi- final on Wednesday and improved on that with her victory a day later.

From BBC ● Aug. 13, 2026

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

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

We walk over the little semi- lunar bridge Baba has built near a cluster of fig trees; it becomes a great suspension bridge joining cities, and the little pond below, a foamy sea.

From "The Kite Runner" by Khaled Hosseini

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

From How to Observe in Archaeology by Various

During the second quarter, traders piled into leveraged products like ETFs to try and cash in on the red-hot rally in semis.

From MarketWatch ● Jul. 28, 2026

When the semis trade started to wobble late last month, many analysts on Wall Street initially hoped the pain would be short-lived.

From MarketWatch ● Jul. 28, 2026

Dyke set the England team two targets: reach the semis of Euro in 2020 and win the World Cup in 2022.

From BBC ● Jul. 13, 2026

Separately, "Strike Norse" embedding a photo of England's Harry Kane and Jude Bellingham, previewing "Lions ready to roar past Norway into the semis" of the World Cup.

From BBC ● Jul. 10, 2026

Several semis blew their horn at me as they went barreling down the highway, and I took this as a criticism that I was not going fast enough.

From "Louisiana's Way Home" by Kate DiCamillo

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