postulator vs asseverator

postulator and asseverator both are nouns.

Word	Noun	Adjective	Verb	Adverb
postulator	Yes	No	No	No
asseverator	Yes	No	No	No

As nouns, asseverator is a hypernym of postulator; that is, asseverator is a word with a broader meaning than postulator:

postulator: someone who assumes or takes something for granted as the basis of an argument
asseverator: someone who claims to speak the truth

Other hypernyms of postulator include affirmer, asserter, avower, declarer.

postulator (noun)	asseverator (noun)
someone who assumes or takes something for granted as the basis of an argument	someone who claims to speak the truth
(Roman Catholic Church) someone who proposes or pleads for a candidate for beatification or canonization