show-off vs poser

show-off and poser both are nouns.

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

As nouns, poser is a hyponym of show-off; that is, poser is a word with a more specific, narrower meaning than show-off:

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

Other hyponyms of show-off include grandstander, hot dog, hotdog, poseur.

show-off (noun)	poser (noun)
someone who deliberately behaves in such a way as to attract attention	a particularly difficult or baffling question or problem
	a person who poses for a photographer or painter or sculptor
	a person who habitually pretends to be something he is not