opine vs guess

opine is not a noun while guess is a noun.

Word	Noun	Adjective	Verb	Adverb
opine	No	No	Yes	No
guess	Yes	No	Yes	No

As verbs, opine and guess are synonyms defined as:

Other synonyms of opine include imagine, reckon, suppose, think.

opine (noun)	guess (noun)
	an estimate based on little or no information
	a message expressing an opinion based on incomplete evidence

opine (verb)	guess (verb)
expect, believe, or suppose	expect, believe, or suppose
express one's opinion openly and without fear or hesitation	judge tentatively or form an estimate of (quantities or time)
	guess correctly; solve by guessing
	put forward, of a guess, in spite of possible refutation