Constantly is from constant plus -ly. Displaced native Old English singallīċe. The suffix -ly recasts constant 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, constantly denotes all the time or very often; again and again. Typical contexts include “The world is constantly changing”. The meaning stays close to the form: it applies the etymological material to all the time or very often; again and again, keeping the visible parts legible in ordinary use.