[sem-ee, sem-ahy]
noun Informal.
semitrailer ( def 1 ).
Often, semis. semifinal ( def 3 ).

by shortening Unabridged


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.

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

See bi-1. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
semi (ˈsɛmɪ)
n , pl semis
1.  (Brit) a semidetached house
2.  short for semifinal
3.  (US), (Canadian), (Austral), (NZ) short for semitrailer

1.  demi- Compare hemi- half: semicircle
2.  partially, partly, not completely, or almost: semiprofessional; semifinal
3.  occurring twice in a specified period of time: semiannual; semiweekly
[from Latin; compare Old English sōm-, sām- half, Greek hēmi-]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

from L. semi- "half," from PIE *semi- (cf. Skt. sami "half," Gk. hemi- "half," O.E. sam-, Goth. sami- "half"). O.E. cognate sam- was used in such compounds as samhal "poor health," lit. "half-whole;" samsoden "half-cooked," figuratively "stupid" (cf. half-baked); samcucu "half-dead," lit. "half-alive;"
and the last survivor of the group, sand-blind "dim-sighted" (q.v.). The Latin-derived form has been common in forming native words since 15c.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

semi- pref.

  1. Half: semicanal.

  2. Partial; partially: semiconscious.

  3. Resembling or having some of the characteristics of: semilunar.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
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 © 2002. Published by Houghton Mifflin. All rights reserved.
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Computing Dictionary

semi definition

/se'mee/ or /se'mi:/ A spoken abbreviation for semicolon.
"Commands to grind are prefixed by semi semi star" means that the prefix is ";;*", not 1/4 of a star.
[Jargon File]

The Free On-line Dictionary of Computing, © Denis Howe 2010
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American Heritage
Abbreviations & Acronyms
  1. semifinal

  2. semitrailer

subendocardial myocardial infarction
The American Heritage® Abbreviations Dictionary, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Example sentences
The adults feed on leaves and leave semi-circular notches on the margins.
Even though we've had some rain, we're still in a semi-arid climate.
The dining room opens onto the semi-walled entrance area.
It is a semi-dwarf and will reach three to four feet tall and wide upon
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