straw poll vs opinion poll

straw poll and opinion poll both are nouns.

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

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

straw poll: an unofficial vote taken to determine opinion on some issue
opinion poll: an inquiry into public opinion conducted by interviewing a random sample of people

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

straw poll (noun)	opinion poll (noun)
an unofficial vote taken to determine opinion on some issue	an inquiry into public opinion conducted by interviewing a random sample of people