semi
noun
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semi
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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”.
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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 /
semi-
2
American
semi-
1
British
prefix
semi
2
British
/ ˈsɛmɪ /
noun
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a semidetached house
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short for semifinal
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short for semitrailer
semi–
Scientific
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 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-
Vocabulary lists containing semi
UCPS 6th Grade Roots List #4
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UCPS 6th Grade Roots List #7
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
“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
They now face Bath on Saturday in a straight shoot-out for a home semi after what has been an impressive season.
From BBC • Jun. 4, 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
Its ecosystem included frogs, lizards, turtles, and mammals such as Patagorhynchus pascuali, a semi aquatic monotreme related to modern echidnas and platypuses.
From Science Daily • May 29, 2026
Then he saw the Chevy slip left again, almost lazily drifting from behind the semi.
From "A Deadly Wandering: A Mystery, a Landmark Investigation, and the Astonishing Science of Attention in the Digital Age" by Matt Richtel
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
