'widely-asserted' is an English compound formed from the adverb 'widely' (the adverbial form of 'wide') and the past participle 'asserted' of the verb 'assert'. 'Wide' ultimately comes from Old English 'wīd' meaning 'broad', while 'assert' comes into English via Old French and Middle English from Latin roots.

'wide' descends from Old English 'wīd' (meaning 'broad'); the adverbial suffix '-ly' formed 'widely'. 'Assert' comes from Latin (past participle 'assertus') via Old French (e.g. 'asserter') into Middle English (e.g. 'asserten') and then modern English 'assert', which yields the past participle 'asserted'. The compound 'widely-asserted' is a modern English formation combining these elements.

The components originally meant 'broad' (for 'wide') and 'to affirm or maintain' (for 'assert'); combined, the phrase has the current meaning 'commonly claimed or affirmed by many'.