straw vote vs opinion poll

straw vote and opinion poll both are nouns.

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

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

straw vote: 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 vote include canvass, poll, public opinion poll.

straw vote (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