'truthfully-declared' originates from the combination of 'truthfully' and 'declared', where 'truthfully' is derived from 'truth' meaning 'conformity to fact or reality', and 'declared' from 'declare', meaning 'to make known or state clearly'.

'truthfully' evolved from Middle English 'trewthe', and 'declare' from Latin 'declarare', which transformed into the Old French 'declarer', eventually becoming the modern English 'declare'.

Initially, 'declare' meant 'to make clear', and 'truthfully' meant 'in a manner of truth', which has largely remained the same in modern usage.