pesadilla
/pesaˈdiʝa/ · A2 · noun · f
bane
😱 pesada (heavy) + -illa: a little heavy thing pressing on the sleeper
From pesar, to weigh, the same root as peso. Old belief held that a bad dream was a weight sitting on the chest, so Spanish named it a small heaviness. The second sense, bane, keeps that idea: a burden that will not lift.