Adequately is from adequate plus -ly. The suffix -ly recasts adequate 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, adequately denotes enough or well enough for a particular purpose. Typical contexts include “Make sure the children are adequately dressed for the cold”. The meaning stays close to the form: it applies the etymological material to enough or well enough for a particular purpose, keeping the visible parts legible in ordinary use.