to form an opinion of or estimate or judge (something) without having sufficient knowledge or information for an accurate assessment
to arrive at a correct conclusion about (something) by conjecture, chance, or intuition
She guessed the answer
chiefly NAmer, informal to believe or suppose (something)
I guess you're right
to make a guess
guessable adj
guesser noun
[Middle English gessen, prob of Scandinavian origin]