postulate

v. presume, suppose; assume, take for granted; claim, stipulate; demand, require

n. assumption, premise; requirement, prerequisite; basic principle, fundamental tenet; axiom, fact that requires no proof

The term postulate, or axiom, indicates a starting assumption from which other statements are logically derived. It does not have to be self-evident (constancy of the speed of light in a vacuum is not self-evident, however it was used as a postulate in the special theory of relativity). Some axioms are experimental facts, but some are just assumptions not based on anything.
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Noun
1. (logic) a proposition that is accepted as true in order to provide a basis for logical reasoning
(synonym) posit
(hypernym) proposition
(hyponym) Bayes' postulate
(derivation) posit
(classification) logic
Verb
1. maintain or assert; "He contended that Communism had no future"
(synonym) contend
(hypernym) claim
2. take as a given; assume as a postulate or axiom; "He posited three basic laws of nature"
(synonym) posit
(hypernym) presuppose, suppose
(hyponym) insist, assert
(derivation) posit
3. require as useful, just, or proper; "It takes nerve to do what she did"; "success usually requires hard work"; "This job asks a lot of patience and skill"; "This position demands a lot of personal sacrifice"; "This dinner calls for a spectacular dessert"; "This intervention does not postulates a patient's consent"
(synonym) necessitate, ask, need, require, take, involve, call for, demand
(hyponym) claim, take, exact
(verb-group) claim, take, exact

n. postulate, assumption, premise, basic principle, fundamental tenet, axiom, fact that requires no proof

v. demand, require; postulate, assume, suppose