'widely-seen' originates from English, combining the adverb 'widely' (from Old English 'wīd' meaning 'wide' with the adverbial suffix '-ly') and 'seen' (the past participle of 'see', from Old English 'seon').

'widely' developed from Old English 'wīd' + adverbial development of '-lic' -> '-ly' in Middle English; 'see' comes from Old English 'seon', producing the past participle form 'seen' in Middle English; the modern compound adjective 'widely-seen' is formed by pairing the adverb with the past participle.

Initially the parts would imply 'seen over a wide area' in a fairly literal sense; over time the compound has come to be used more generally as 'seen by many people' or 'widely known/ circulating'.