'commonly-discussed' is a compound formed from 'commonly' and 'discussed'. 'commonly' ultimately comes from Latin 'communis' (via Old French 'comun' and Middle English 'commune'), where the root 'com-' meant 'together' and 'munis' related to 'service' or 'shared'. 'discussed' comes from Latin 'discutere' (via Medieval/Latin usage and Old French), where the prefix 'dis-' meant 'apart' and 'quatere' (or 'quassare') meant 'to shake'.

'commonly' developed from Latin 'communis' → Old French 'comun' → Middle English 'commune/commen' and became the adverbial form 'commonly'. 'discutere' in Latin passed into Medieval Latin/Old French as forms like 'discuter' and entered English as 'discuss' (past participle 'discussed'), and combining 'commonly' + 'discussed' produced the modern compound adjective 'commonly-discussed'.

Originally, elements meant 'shared/together' (from 'communis') and 'to shake apart' or 'examine' (from 'discutere'); over time 'discuss' shifted to the sense 'to talk about or examine a subject', and the compound now simply means 'frequently talked about'.