'Surmise' was a legal term for an accusation 'thrown upon' someone — it weakened to uncertain conjecture.
To suppose that something is true without having evidence to confirm it; a supposition based on incomplete evidence.
From Anglo-French surmise (an accusation, a charge), past participle of Old French surmettre (to accuse, charge, throw upon), from Latin supermittere (to send over, throw upon), from super- (over, upon) + mittere (to send, to throw). The original sense was a formal legal accusation — something thrown upon someone before proof was established. The shift from accusation to mere conjecture reflects the weakening of epistemic certainty: from alleging a fact against someone, to merely guessing. The same Latin mittere underlies
Keats used 'surmise' in one of English poetry's most famous lines: 'Then felt I like some watcher of the skies / When a new planet swims into his ken; / Or like stout Cortez when with eagle eyes / He star'd at the Pacific — and all his men / Look'd at each other with a wild surmise.' The word perfectly captures the state between seeing and knowing — the moment of unconfirmed recognition.