'well-read' originates from the English adverb 'well' (Old English 'wel') meaning 'in a good way' combined with the past participle 'read' (from Old English 'rǣdan') meaning 'to read/interpret'.

'rǣdan' developed into Middle English 'reden'/'readen' and then modern English 'read'; the compound combination of 'well' + past participle 'read' produced the adjectival phrase 'well-read' in Early Modern English to describe someone extensively read.

Initially it described someone who had been 'read well' (i.e., instructed or informed by reading); over time it stabilized into the adjectival sense 'having wide knowledge from reading', which is still the current meaning.