epoch vs epochal

epoch is a noun but epochal is not a noun.

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

epoch (noun)	epochal (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

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