public opinion poll vs enquiry

public opinion poll and enquiry both are nouns.

Word	Noun	Adjective	Verb	Adverb
public opinion poll	Yes	No	No	No
enquiry	Yes	No	No	No

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

public opinion poll: an inquiry into public opinion conducted by interviewing a random sample of people
enquiry: a search for knowledge

Other hypernyms of public opinion poll include inquiry, research.

public opinion poll (noun)	enquiry (noun)
an inquiry into public opinion conducted by interviewing a random sample of people	a systematic investigation of a matter of public interest
	a search for knowledge
	an instance of questioning