'much-watched' originates from English, specifically from the adjective 'much' and the past participle 'watched' (from the verb 'watch'), where 'much' ultimately comes from Old English 'micel'/'mycel' meaning 'great, large, many' and 'watch' comes from Old English 'wæccan' meaning 'to be awake; to watch'.

'much' changed from Old English 'micel'/'mycel' to Middle English 'muche' and eventually to modern English 'much'; 'watch' changed from Old English 'wæccan' (verb) and noun forms like 'wæcce' into Middle English 'wacchen'/'watchen' and then modern English 'watch' with the past participle 'watched', and the compound adjective 'much-watched' is formed by combining them.

Initially, 'much' meant 'great in quantity' and 'watch' originally meant 'to be awake or keep vigil' (later shifting to 'observe'); over time 'watch' came to mean 'observe', and the combined form 'much-watched' evolved to mean 'observed by many' or 'attracting a large viewing audience'.