imitation vs postiche

imitation and postiche both are nouns.

Word	Noun	Adjective	Verb	Adverb
imitation	Yes	Yes	No	No
postiche	Yes	No	No	No

As nouns, postiche is a hyponym of imitation; that is, postiche is a word with a more specific, narrower meaning than imitation:

Other hyponyms of imitation include fake, sham, counterfeit, forgery.

imitation (noun)	postiche (noun)
copying (or trying to copy) the actions of someone else	something that is a counterfeit; not what it seems to be
something copied or derived from an original	a covering or bunch of human or artificial hair used for disguise or adornment
the doctrine that representations of nature or human behavior should be accurate imitations
a representation of a person that is exaggerated for comic effect

imitation (adjective)	postiche (adjective)
not genuine or real; being an imitation of the genuine article