Sisyphean vs Sisyphus

Sisyphean is not a noun while Sisyphus is a noun.

Word	Noun	Adjective	Verb	Adverb
Sisyphean	No	Yes	No	No
Sisyphus	Yes	No	No	No

Sisyphean (noun)	Sisyphus (noun)
	(Greek legend) a king in ancient Greece who offended Zeus and whose punishment was to roll a huge boulder to the top of a steep hill; each time the boulder neared the top it rolled back down and Sisyphus was forced to start again

Sisyphean (adjective)	Sisyphus (adjective)
of or relating to Sisyphus
both extremely effortful and futile