detective story vs whodunit

detective story and whodunit both are nouns.

Word	Noun	Adjective	Verb	Adverb
detective story	Yes	No	No	No
whodunit	Yes	No	No	No

As nouns, whodunit is a hypernym of detective story; that is, whodunit is a word with a broader meaning than detective story:

detective story: a narrative about someone who investigates crimes and obtains evidence leading to their resolution
whodunit: a story about a crime (usually murder) presented as a novel or play or movie

Other hypernyms of detective story include mystery, mystery story.

detective story (noun)	whodunit (noun)
a narrative about someone who investigates crimes and obtains evidence leading to their resolution	a story about a crime (usually murder) presented as a novel or play or movie