"sourness of temper, sullenness," 1660s, from morose + -ness. Earlier in the same sense was morosity (1530s), from French morosité, from Latin morositas.
Entries linking to moroseness
morose adj.
1530s "gloomy, of a sour temper, sullen and austere," from Latin morosus "morose, peevish, hypercritical, fastidious," from mos (genitive moris) "habit, custom" (see moral (adj.)). In English, manners by itself means "(good) manners," but here the implication in Latin is "(bad) manners."
-ness
word-forming element denoting action, quality, or state, attached to an adjective or past participle to form an abstract noun, from Old English -nes(s), from Proto-Germanic *in-assu- (cognates: Old Saxon -nissi, Middle Dutch -nisse, Dutch -nis, Old High German -nissa, German -nis, Gothic -inassus), from *-in-, originally belonging to the noun stem, + *-assu-, abstract noun suffix, probably from the same root as Latin -tudo (see -tude).