'rapidly-changing' originates from the combination of 'rapidly' and 'changing', where 'rapidly' comes from Latin 'rapidus' meaning 'swift' and 'changing' from Old French 'changier' meaning 'to alter'.

'rapidly' evolved from the Latin 'rapidus' through Old French 'rapide', and 'changing' from Old French 'changier', eventually forming the modern English term 'rapidly-changing'.

Initially, 'rapidly' meant 'swiftly' and 'changing' meant 'altering', and together they have maintained the meaning of 'undergoing swift alteration'.