poser vs sitter

poser and sitter both are nouns.

Word	Noun	Adjective	Verb	Adverb
poser	Yes	No	No	No
sitter	Yes	No	No	No

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

Other hyponyms of poser include artist's model, dressmaker's model, photographer's model.

poser (noun)	sitter (noun)
a particularly difficult or baffling question or problem	a domestic hen ready to brood
a person who poses for a photographer or painter or sculptor	a person engaged to care for children when the parents are not home
a person who habitually pretends to be something he is not	an organism (person or animal) that sits
	a person who poses for a painter or sculptor