Literally, a casting or throwing together of possible or probable events; or a casting of the mind to something future, or something past but unknown; a guess, formed on a supposed possibility or probability of a fact, or on slight evidence; preponderance of opinion without proof; surmise. We speak of future or unknown things by conjecture, and of probable or unfounded conjectures.

Idea; notion.

To guess; to judge by guess, or by the probability or the possibility of a fact, or by very slight evidence; to form an opinion at random. What will be the issue of a war, we may conjecture, but cannot know. He conjectured that some misfortune had happened.