sitter vs keeper

sitter and keeper both are nouns.

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

As nouns, keeper is a hypernym of sitter; that is, keeper is a word with a broader meaning than sitter:

sitter (noun)	keeper (noun)
a domestic hen ready to brood	one having charge of buildings or grounds or animals
a person engaged to care for children when the parents are not home	someone in charge of other people
an organism (person or animal) that sits
a person who poses for a painter or sculptor