conjecture

Short definition from Wiktionary

Noun

1. 1
   A statement or an idea which is unproven, but is thought to be true; a guess.
2. 2
   A supposition based upon incomplete evidence; a hypothesis.
3. 3
   A statement likely to be true based on available evidence, but which has not been formally proven.
4. 4
   Interpretation of signs and omens.

Verb

1. 1
   To guess; to venture an unproven idea.
2. 2
   To infer on slight evidence; to guess at.