olemus
Merriam-Webster:
1: to form an opinion of from little or no evidence
// She could only guess what he meant.
2: BELIEVE, SUPPOSE
// I guess you're right

as a guess -- oletatavasti
blind guess -- huupi oletus
educated guess -- põhjendatud arvamus
guesswork -- oletus; ennustamine
to make a guess -- oletama
wild guess -- huupi oletus