The compound "well-baby" is a modern English formation, combining two native English elements to create a specific medical and parental care term. The word "well" derives from the Proto-Germanic wel, carrying the core sense of "wish" or "good," which evolved into its adverbial and adjectival uses denoting satisfactory or healthy states. "Baby" originates as a reduplicative nursery word, common across many languages to denote an infant. The compound logic is transparently descriptive: it literally denotes a "healthy infant," but its specific application emerged in the 20th century within the context of preventative pediatric healthcare, distinguishing routine checkups for healthy children from sick visits.

Structure: well (healthy) + baby (infant) - well: From Old English wel, meaning "in a good way, satisfactorily, properly." In this compound, it functions as an adjective meaning "healthy" or "in good condition." - baby: From Middle English babi, an imitative or child-talk word. It functions as a noun meaning "a very young child."