The compound adjective 'well-acquainted' is built upon the verb 'acquaint', which entered English via Old French from the Latin verb cognoscere, meaning 'to get to know' or 'to recognize'. The prefix 'well-' is of Germanic origin and functions as an intensifier, adding the sense of thoroughness or completeness to the state described. Therefore, the literal construction 'thoroughly made known' logically evolved to describe a person who is thoroughly familiar or knowledgeable about a subject or another person. The '-ed' suffix solidifies this as an adjective describing a state of being.

Structure: well (thoroughly) + acquaint (make known) + ed (adjective suffix) - well: Old English; an adverb used as an intensifier meaning 'thoroughly', 'properly', or 'fully'. - acquaint: From Old French acointer, based on Latin accognitare, from ad- 'to' + cognitus, past participle of cognoscere 'know'; the verb meaning 'to make known' or 'to make familiar'. - ed: Old English; a suffix forming adjectives from verbs, indicating a state or condition.