postulator vs declarer

postulator and declarer both are nouns.

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

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

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

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

postulator (noun)	declarer (noun)
someone who assumes or takes something for granted as the basis of an argument	the bridge player in contract bridge who wins the bidding and can declare which suit is to be trumps
(Roman Catholic Church) someone who proposes or pleads for a candidate for beatification or canonization	someone who claims to speak the truth