The compound adjective 'well-attended' is a relatively modern formation built from native English elements. The core verb 'attend' originates from the Latin 'attendere', meaning 'to stretch toward' or 'give heed to', which evolved through Old French into its modern sense of being present. The intensifying adverb 'well', from Old English 'wel' meaning 'in a good manner', is prefixed to the past participle 'attended' to create a descriptive term. The logical construction is transparent: an event that has been 'attended' (had people present) in a 'well' (good, thorough) manner, thus signifying a large or satisfactory turnout.

Structure: well (to a good degree) + attend (be present) + ed (adjective suffix) - well: Old English; an adverb used here as an intensifying prefix meaning 'thoroughly' or 'to a good degree'. - attend: Latin via Old French; a verb root meaning 'to stretch toward, give heed to, be present at'. - ed: Old English; a suffix forming past participles and participial adjectives.