sulk

Back-formation from sulky, of uncertain origin. Probably from Middle English sulke, solke (attested in solcenesse (“idleness; laziness”), from Old English āsolcennys (“idleness; slothfulness; sluggishness; laziness”), from āsolcen (“sulky, languid”), from past participle of Old English āseolcan (“be slow; be weak or slothful; languish”), from Proto-Germanic selkaną (“to fall in drops; dribble; droop”), from Proto-Indo-European sélǵ-o-nom, from selǵ- (“to let go, send”). Cognate with several Indo-Iranian words deriving from Proto-Indo-Iranian sarȷ́- (such as Sanskrit सृजति (sṛjáti), सर्जन (sárjana), सृक (sṛká)), possibly Hittite 𒊭𒀠𒀝𒍣 (ša-al-ak-zi /⁠šalkzi⁠/, “knead, mix”), although the semantic connection is weak.

From Latin sulcus.