poser vs show-off

poser and show-off both are nouns.

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

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

poser: 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 poser include exhibitionist.

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