poseur vs show-off

poseur and show-off both are nouns.

Word	Noun	Adjective	Verb	Adverb
poseur	Yes	No	No	No
show-off	Yes	No	No	No

As nouns, show-off is a hypernym of poseur; that is, show-off is a word with a broader meaning than poseur:

poseur: a person who habitually pretends to be something he is not
show-off: someone who deliberately behaves in such a way as to attract attention

Other hypernyms of poseur include exhibitionist.

poseur (noun)	show-off (noun)
a person who habitually pretends to be something he is not	someone who deliberately behaves in such a way as to attract attention