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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

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

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, Musk walked back earlier guidance on the rollout of its Robotaxi ride-hailing service, Optimus humanoid robots and an electric semi truck that has been in development for years.

From The Wall Street Journal ● Jul. 23, 2026

Holy Trinity Tattoo Studio in Standish managed to squeeze Sean in before England took on Norway in the quarter final, teeing up Wednesday night's mouth-watering semi against old foes Argentina.

From BBC ● Jul. 15, 2026

Johnny Beig may have played in a semi professional cricket league in Australia, but this summer he’s a big fan of soccer in the United States.

From Los Angeles Times ● Jul. 3, 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

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.

From Los Angeles Times ● Nov. 20, 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

Huckabee’s shift from semi- retirement to being on the cusp of another presidential run began in July 2013, based on interviews with his allies in November and on Saturday.

From Washington Post ● Jan. 3, 2015

These had been grown elsewhere, because few crops could be raised in the dry semi- desert region of Loun-Ariik.

From "A Long Walk to Water" by Linda Sue Park

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

From How to Observe in Archaeology by Various

Ben Shelton to the semis 🔥 Shelton outlasts the defending champion Alcaraz in a five-set thriller!

From Los Angeles Times ● Sep. 9, 2026

Those three should be in the semis unless they meet before.

From BBC ● Sep. 7, 2026

But the most unexpected part of the Three Lions’ march to the semis is that it wasn’t built on the might of the Premier League.

From The Wall Street Journal ● Jul. 15, 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

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