axiom vs apothegm

axiom and apothegm both are nouns.

Word	Noun	Adjective	Verb	Adverb
axiom	Yes	No	No	No
apothegm	Yes	No	No	No

As nouns, apothegm is a hyponym of axiom; that is, apothegm is a word with a more specific, narrower meaning than axiom:

Other hyponyms of axiom include aphorism, apophthegm, gnome, moralism.

axiom (noun)	apothegm (noun)
a saying that is widely accepted on its own merits	a short pithy instructive saying
(logic) a proposition that is not susceptible of proof or disproof; its truth is assumed to be self-evident