Why was clemency trending last week?
"sullen," 1744, probably from Old English asolcen "idle, lazy, slow," from past participle of aseolcan "become sluggish, be weak or idle" (related to besylcan "be languid"), from Proto-Germanic *seklanan (cf. Middle High German selken "to drop, fall").
"light carriage with two wheels," 1756, apparently a noun use of sulky (adj.), on notion of "standoffishness," because the carriage has room for only one person.