The compound adjective 'well-informed' is a transparent combination of native English elements. The adverb 'well', with Proto-Germanic roots meaning "wished-for, good," intensifies the state described by 'informed'. The core concept of 'informed' originates from the Latin verb informare, which literally meant "to shape or form within," evolving through Old French to mean "to instruct or give knowledge to." Thus, the literal construction "shaped well from within" elegantly captures the modern abstract sense of possessing thorough and accurate knowledge on a subject, as if one's mind has been properly furnished with information.

Structure: well (to a good degree) + informed (having knowledge) - well: From Old English wel, meaning "in a good way, satisfactorily, properly." It functions as an adverb modifying the adjective 'informed' to indicate a high degree or quality. - informed: From the past participle of the verb inform, itself from Latin informare ("to shape, give form to, instruct"). In this compound, it functions as an adjective meaning "having knowledge or information."