Conjecture as a noun is used to mean inference or judgment which is based on evidence that is inconclusive or incomplete. It generally means guesswork. It could be a statement, an opinion, or a conclusion that is based on guesswork. The term, at one point in time, used to mean interpretation of omens. A conjecture, in mathematics, is a mathematical statement that seems likely to be true.
The word is believed to have come from the Latin term conjectura, which comes from conjectus. Conjectus is the past participle of conicere, which literally means to throw together. This word is formed by com- + jacere, meaning 'to throw'.
The verb forms are conjectured, conjecturing and conjectures where as a transitive verb it would mean to infer from evidence that inconclusive; or to guess. As an intransitive verb it can be used to mean 'to make a conjecture.'