- a combining form appearing in loanwords from French meaning “half” (demilune), “lesser” (demitasse), or sometimes used with a pejorative sense (demimonde); on this model, also prefixed to words of English origin (demigod).
Origin of demi-
< French, combining form representing demi (adj.; also noun and adv.) < Vulgar Latin *dīmedius, for Latin dīmidius half, equivalent to dī- di-2 + medius middle
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via French from Medieval Latin dīmedius, from Latin dīmīdius half, from dis- apart + medius middle
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
Word Origin and History for demi-
Online Etymology Dictionary, © 2010 Douglas Harper
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.