The Collaborative International Dictionary
Dys- \Dys-\ An inseparable prefix, fr. the Greek dys- hard, ill, and signifying ill, bad, hard, difficult, and the like; cf. the prefixes, Skr. dus-, Goth. tuz-, OHG. zur-, G. zer-, AS. to-, Icel. tor-, Ir. do-. [1913 Webster] ||
Douglas Harper's Etymology Dictionary
word-forming element meaning "bad, ill, abnormal," from Greek dys-, inseparable prefix "destroying the good sense of a word or increasing its bad sense" [Liddell & Scott], "bad, hard, unlucky," from PIE root (and prefix) *dus- "bad, ill, evil" (cognates: Sanskrit dus-, Old Persian duš- "ill," Old English to-, Old High German zur-, Gothic tuz- "un-"), a derivative of the root *deu- (1) "to lack, be wanting" (source of Greek dein "to lack, want").\n
\nVery productive in ancient Greek, where it could attach even to proper names (such as dysparis "unhappy Paris"); its entries take up nine columns in Liddell and Scott. Among the words formed from it were some English might covet: dysouristos "fatally favorable, driven by a too-favorable wind;" dysadelphos "unhappy in one's brothers;" dysagres "unlucky in fishing;" dysantiblepos "hard to look in the face."