1) Effortful 2) Useless 1) Endless and difficult 2) Futile on a grand scale 3) Mythical being 
laborious, endless and futile
• (a.) Relating to Sisyphus; incessantly recurring; as, Sisyphean labors.
Sis`y·phe'an adjective Relating to Sisyphus; incessantly recurring; as, Sisyphean labors. 
[adj] - of or relating to Sisyphus 2. [adj] - both extremely effortful and futile
Sisyphean Sisyphus, a crafty king of ancient Corinth. A reference to endless heartbreaking toil when anyone is engaged in Sisyphean work. The term comes from the legend of Sisyphus, an ancient king of Corinth, who was sent to Hades for crimes against his subjects and condemned forever to roll a huge stone up a steep hill, only to have it roll down...
adjective both extremely effortful and futile
[Obscure words] both extremely effortful and futile