whodunit vs mystery

whodunit and mystery both are nouns.

Word	Noun	Adjective	Verb	Adverb
whodunit	Yes	No	No	No
mystery	Yes	No	No	No

As nouns, whodunit and mystery are synonyms defined as:

whodunit and mystery: a story about a crime (usually murder) presented as a novel or play or movie

Other synonyms of whodunit include mystery story.

whodunit (noun)	mystery (noun)
a story about a crime (usually murder) presented as a novel or play or movie	something that baffles understanding and cannot be explained
	a story about a crime (usually murder) presented as a novel or play or movie