postiche vs wig

postiche and wig both are nouns.

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

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

postiche: a covering or bunch of human or artificial hair used for disguise or adornment
wig: hairpiece covering the head and made of real or synthetic hair

Other hyponyms of postiche include Afro-wig, switch, toupe, toupee.

postiche (noun)	wig (noun)
something that is a counterfeit; not what it seems to be	hairpiece covering the head and made of real or synthetic hair
a covering or bunch of human or artificial hair used for disguise or adornment	British slang for a scolding