The word 'unhealthily' is a modern English formation built upon the foundational concept of 'health,' which originates from the Old English hǣlþ, itself derived from the Proto-Germanic hailithō, meaning "wholeness" or "soundness." The negative prefix un-, one of the most common and ancient negators in the language, is attached to form the adjective 'unhealthy,' literally meaning "not in a state of wholeness." Finally, the adverbial suffix -ly, historically meaning "having the body or form of," is appended to create the adverb specifying the manner of an action. Thus, the term's logic moves from the ancient ideal of completeness (hailithō) to its negation and finally to the characterization of an action performed in a way that departs from that state of soundness.

Structure: un (not) + health (state of well-being) + ily (manner adverb suffix) - un: A prefix of Germanic origin (Old English un-), meaning "not." It functions as a negative particle. - health: A noun of Germanic origin (Old English hǣlþ), meaning "wholeness, soundness, well-being." It functions as the core substantive root. - ily: An adverbial suffix, a variant of -ly (from Old English -līce), attached to the adjective form unhealthy. It indicates the manner or way in which an action is performed.