Abruptly is from abrupt plus -ly. The suffix -ly recasts abrupt as an adverb: the lexical idea remains recognizable, but the word now describes manner, degree, or circumstance rather than naming the quality by itself. In use as an adverb, abruptly denotes suddenly and without warning. Typical contexts include “The professor stopped abruptly when the lights went out”. The meaning stays close to the form: it applies the etymological material to suddenly and without warning, keeping the visible parts legible in ordinary use.