'much-used' is a compound of 'much' and 'used'. 'Much' originates from Old English, specifically the word 'mycel', where 'mycel' meant 'great, large'. 'Used' comes from Old French 'user' (from Latin 'uti'), where 'uti' meant 'to use'. The compound form is a Modern English formation combining these elements to describe frequent or extensive use.

'much' changed from Old English 'mycel' and developed into Middle and Modern English 'much'; 'use' evolved from Latin 'uti' to Old French 'user' and Middle English 'usen'/'use', and the adjectival compound 'much-used' arose in Modern English by combining the adverb/quantifier with the past-participial adjective.

Initially, the parts conveyed 'great' (much) and 'employed' (used); over time the compound took on the specific senses 'frequently used' and 'worn by frequent use' in modern usage.