1. Something demanded or asserted; especially, a position or supposition assumed without proof, or one which is considered as self–evident; a truth to which assent may be demanded or challenged, without argument or evidence.
2. (Science: geometry) The enunciation of a self–evident problem, in distinction from an axiom, which is the enunciation of a self-evident theorem. The distinction between a postulate and an axiom lies in this, that the latter is admitted to be self-evident, while the former may be agreed upon between two reasoners, and admitted by both, but not as proposition which it would be impossible to deny. (eng. Cyc)
Origin: L. Postulatum a demand, request, prop. P. P. Of postulare to demand, prob. A dim. Of poscere to demand, prob. For porcscere; akin to G. Forschen to search, investigate, Skr. Prach to ask, and L. Precari to pray: cf. F. Postulat. See Pray.