"pertaining to or resembling the unceasingly recurring and fruitless labors of Sisyphus," 1630s, from Sisyphus + -an. The earlier form was Sisyphian (1590s).
Entries linking to sisyphean
Sisyphus
King of Corinth in classical mythology, famed as "the craftiest of men," he was condemned in the afterlife to roll uphill a stone which perpetually rolls down again; from Latinized form of Greek Sisyphos, a name of unknown origin. Liddell & Scott suggest a reduplication of syphos "the crafty" (with Aeolic -u- for -o-), but Klein calls this folk-etymology.
-an
word-forming element meaning "pertaining to," from Latin -anus, adjective suffix, in some cases via French -ain, -en. From PIE *-no-.