Adversely is from adverse plus -ly. The suffix -ly recasts adverse 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, adversely denotes in a way that has a bad or harmful effect. Typical contexts include “The company was adversely affected by the new regulations”. The meaning stays close to the form: it applies the etymological material to in a way that has a bad or harmful effect, keeping the visible parts legible in ordinary use.