postiche vs toupee

postiche and toupee both are nouns.

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

As nouns, toupee is a hyponym of postiche; that is, toupee 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
toupee: a small hairpiece to cover partial baldness

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

postiche (noun)	toupee (noun)
something that is a counterfeit; not what it seems to be	a small hairpiece to cover partial baldness
a covering or bunch of human or artificial hair used for disguise or adornment