rebuff vs pooh-pooh

rebuff is a noun but pooh-pooh is not a noun.

Word	Noun	Adjective	Verb	Adverb
rebuff	Yes	No	Yes	No
pooh-pooh	No	No	Yes	No

As verbs, pooh-pooh is a hypernym of rebuff; that is, pooh-pooh is a word with a broader meaning than rebuff:

Other hypernyms of rebuff include disdain, freeze off, reject, scorn, spurn, turn down.

rebuff (noun)	pooh-pooh (noun)
a deliberate discourteous act (usually as an expression of anger or disapproval)
an instance of driving away or warding off

rebuff (verb)	pooh-pooh (verb)
reject outright and bluntly	reject with contempt
force or drive back	express contempt about