Word Origin & History
early 13c., from O.Fr. gelos (12c., Fr. jaloux), from L.L. zelosus, from zelus "zeal," from Gk. zelos, sometimes "jealousy," but more often in a good sense ("emulation, rivalry, zeal"). See zeal. Among the ways to express this are Swed. svartsjuka, lit. "black-sick," from phrase bara svarta strumpor
"wear black stockings," also "be jealous." Dan. skinsyg "jealous," lit. "skin-sick," is from skind "hide, skin" said to be explained by Swed. dial. expression fa skinn "receive a refusal in courtship."
"Most of the words for 'envy' ... had from the outset a hostile force, based on 'look at' (with malice), 'not love,' etc. Conversely, most of those which became distinctive terms for 'jealousy' were originally used also in a good sense, 'zeal, emulation.' " [Buck, pp.1138-9]