[ sem-ee, sem-ahy ]
/ ˈsɛm i, ˈsɛm aɪ /
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See synonyms for: semi / semis on Thesaurus.com

noun Informal.
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Origin of semi

By shortening

Other definitions for semi (2 of 2)


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.

Origin of semi-

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

words often confused with semi-

See bi-1.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


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.

Examples of semi-

An example of a word you may have encountered that features semi– is semicolon, “the punctuation mark (;).”

We know semi– means “half,” and a colon is the sign (:). The word colon itself comes from Greek kôlon, meaning “limb; part of a clause or period.” Semicolon literally translates to “half colon.”

What are some words that use the combining form semi-?

What are some other forms that semi– may be commonly confused with?

Break it down!

The word literate means “able to read and write.” With this in mind, what does semiliterate mean?

How to use semi in a sentence

British Dictionary definitions for semi (1 of 2)

/ (ˈsɛmɪ) /

noun plural semis
British a semidetached house
short for semifinal
US, Canadian, Australian and NZ short for semitrailer

British Dictionary definitions for semi (2 of 2)


halfsemicircle Compare demi- (def. 1), hemi-
partially, partly, not completely, or almostsemiprofessional; semifinal
occurring twice in a specified period of timesemiannual; semiweekly

Word Origin for semi-

from Latin; compare Old English sōm-, sām- half, Greek hēmi-
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for semi


A prefix that means “half,” (as in semicircle, half a circle) or “partly, somewhat, less than fully,” (as in semiconscious, partly conscious).
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.