'well-looking' is a compound formed from the adverb/adjunct 'well' (Old English 'wel') and the present participle/verb 'look' (Old English 'lōcian' / 'locian'), used together to mean 'having a good look' or 'appearing well'.

'well' comes from Old English 'wel' (from Proto-Germanic *welaz) meaning 'well' or 'in a good way'; 'look' derives from Old English 'lōcian' (to look) and Middle English forms like 'loken'/'loken'. The compound construction 'well-looking' follows English compounding patterns (adverb/adjective + participle/adjective) and has been used analogously to 'good-looking' in later English.

Initially a literal combination meaning 'appearing in a good way' or 'having a good appearance'; over time it has been used idiomatically to mean simply 'attractive' or 'good-looking' in everyday speech.