Sisyphean

[adj] - of or relating to Sisyphus 2. [adj] - both extremely effortful and futile
Found on http://www.webdictionary.co.uk/definition.php?query=Sisyphean

Sisyphean

Sis`y·phe'an adjective Relating to Sisyphus; incessantly recurring; as, Sisyphean labors.
Found on http://www.encyclo.co.uk/webster/S/110

Sisyphean

adjective both extremely effortful and futile
Found on https://www.encyclo.co.uk/local/20974

Sisyphean

• (a.) Relating to Sisyphus; incessantly recurring; as, Sisyphean labors.
Found on http://thinkexist.com/dictionary/meaning/sisyphean/

Sisyphean

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...
Found on http://www.wordinfo.info/words/index/info/view_unit/3481/6

sisyphean

laborious, endless and futile
Found on http://phrontistery.info/s.html

Sisyphean

both extremely effortful and futile
Found on https://www.vocabulary.com/lists/2365341
No exact match found