WordReference Random House Learner's Dictionary of American English © 2017
demi- comes from French, where it has the meaning "half.'' This meaning is found in such words as: demigod, demitasse.
WordReference Random House Unabridged Dictionary of American English © 2017
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).
- Vulgar Latin *dīmedius, for Latin dīmidius half, equivalent. to dī- di-2 + medius middle
- French, combining form representing demi (adjective, adjectival; also noun, nominal and adverb, adverbial)
Collins Concise English Dictionary © HarperCollins Publishers::
Etymology: via French from Medieval Latin dīmedius, from Latin dīmīdius half, from dis- apart + medius middle
- half: demirelief
- of less than full size, status, or rank: demigod
'demi-' also found in these entries: