semi-

¹ 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 ² American  

[sem-ee, sem-ahy] / ˈsɛm i, ˈsɛm aɪ /

noun

Informal.

1. semitrailer.

2. Often semifinal.

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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.

Etymology

Origin of semi-¹

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

Origin of semi¹

By shortening

Example Sentences

He made the semis at all four majors in 2025 but failed to go further, with his last Grand Slam title coming at the US Open in 2023.

From Barron's

Now 38, he has had to settle for a secondary role since Sinner and Alcaraz took control of the men's tour, making the semis at all four majors in 2025 but not going further.

From Barron's

He surged into the top five after reaching the US Open semis, claiming the Brussels title and losing to Sinner in the Paris Masters final.

From BBC

While Hawkins replied with a wonderful break of 138, Selby sealed his success with a run of 83 to reach the semis for the first time since 2016 - the year of his second UK success.

From BBC

England and Ireland would also be kept apart from each other until the semis, while the Springboks and All Blacks would be on a quarter-final collision course, ensuring one would fall before the last four.

From BBC