epochal vs epoch

epochal is not a noun while epoch is a noun.

Word	Noun	Adjective	Verb	Adverb
epochal	No	Yes	No	No
epoch	Yes	No	No	No

epochal (noun)	epoch (noun)
	a period marked by distinctive character or reckoned from a fixed point or event
	a unit of geological time that is a subdivision of a period and is itself divided into ages
	(astronomy) an arbitrarily fixed date that is the point in time relative to which information (as coordinates of a celestial body) is recorded

epochal (adjective)	epoch (adjective)
highly significant or important especially bringing about or marking the beginning of a new development or era