supposition, suppose, hypothesis, surmise, hypothesize, speculate, guess, speculation, theorize, hypothecate, more...

fact, certainty, truth

hypothesis, speculation, assumption, postulation, guess, conclusion, theory, proposition, more...

mere, pure, probable, only, much, reasonable, plausible, vague, ingenious, wild, interesting

guess or hypothesis,   a guess,   guess work,   stabwild guess,   suppose guess,   semi-educated guess,   to surmise,   lack of proof,   think suppose,   baseless assumption