exit poll vs opinion poll

exit poll and opinion poll both are nouns.

Word	Noun	Adjective	Verb	Adverb
exit poll	Yes	No	No	No
opinion poll	Yes	No	No	No

As nouns, opinion poll is a hypernym of exit poll; that is, opinion poll is a word with a broader meaning than exit poll:

exit poll: a poll of voters as they leave the voting place; usually taken by news media in order to predict the outcome of an election
opinion poll: an inquiry into public opinion conducted by interviewing a random sample of people

Other hypernyms of exit poll include canvass, poll, public opinion poll.

exit poll (noun)	opinion poll (noun)
a poll of voters as they leave the voting place; usually taken by news media in order to predict the outcome of an election	an inquiry into public opinion conducted by interviewing a random sample of people