To reach a partly (or totally) unqualified conclusion.
To solve by a correct conjecture; to conjecture rightly.
He who guesses the riddle shall have the ring.
To suppose (introducing a proposition of uncertain plausibility).
That album is quite hard to find, but I guess you could try ordering it online.
To think, conclude, or decide (without a connotation of uncertainty). Usually in first person: "I guess".
"I guess I'll go to bed."
To hit upon or reproduce by memory.
A prediction about the outcome of something, typically made without factual evidence or support.
If you don't know the answer, take a guess.