austere vs ascetic

austere is not a noun while ascetic is a noun.

Word	Noun	Adjective	Verb	Adverb
austere	No	Yes	No	No
ascetic	Yes	Yes	No	No

As adjectives, austere and ascetic are synonyms defined as:

Other synonyms of austere include ascetical, spartan.

austere (noun)	ascetic (noun)
	someone who practices self denial as a spiritual discipline

austere (adjective)	ascetic (adjective)
practicing great self-denial	pertaining to or characteristic of an ascetic or the practice of rigorous self-discipline
of a stern or strict bearing or demeanor; forbidding in aspect	practicing great self-denial
severely simple