Etymology: < French demi < Latin dīmidium half: see dimidiate adj. The French word is a noun and adjective, and much used in combination. It began to be used in English in the 15th cent. attributive in Heraldry, and in the 16th cent. in names of cannon, and soon passed to other uses. At first it was often written separately; hence it was also treated as a simple adjective, and occasionally as a noun. (In certain uses the separate word survives as demy n.) But demi- is now almost always hyphenated to the word which it qualifies, and it has become to a large extent a living element, capable of being prefixed to almost any noun (often also to adjectives, and sometimes to verbs).