(formal) A statement or an idea which is unproven, but is thought to be true; a guess.

(formal) A supposition based upon incomplete evidence; a hypothesis.

(mathematics, linguistics) A statement likely to be true based on available evidence, but which has not been formally proven.

(formal, intransitive) To guess; to venture an unproven idea.

(transitive) To infer on slight evidence; to guess at.