supposition

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The act of supposing.
2. n. Something supposed; an assumption.

Century Dictionary and Cyclopedia

1. n. The act and mental result of hypothetical inference; that act of mind by which a likelihood is admitted in a proposition on account of the truth of its consequences; a presumption.
2. n. The act and mental result of formulating a proposition, without reference to its truth or falsity, for the sake of tracing out its consequences; a hypothesis.
3. n. In logic, the way in which a name is to be understood in a given proposition, in reference to its standing for an object of this or that class. Thus, in the sentences “man is a biped,” “man has turned rivers and cut through mountains,” “man is a class name,” the substantive name man has the same signification but different suppositions. The signification is said to be the same, because the variations of meaning are merely the regular variations to which names are generally subject; and these general modes of variation of meaning are called suppositions.
4. n. Substitution.
5. n. See the adjectives.

Wiktionary

1. n. Something that is supposed; an assumption made to account for known facts, conjecture
2. n. The act or an instance of supposing

GNU Webster's 1913

1. n. The act of supposing, laying down, imagining, or considering as true or existing, what is known not to be true, or what is not proved.
2. n. That which is supposed; hypothesis; conjecture; surmise; opinion or belief without sufficient evidence.

WordNet 3.0

1. n. a message expressing an opinion based on incomplete evidence
2. n. a hypothesis that is taken for granted
3. n. the cognitive process of supposing