'assuasive' ultimately originates from Latin elements related to 'suavis' (meaning 'sweet' or 'pleasant'), via verbs formed from that root meaning 'to make pleasant' or 'to soften'.

'assuasive' developed from Middle English and Old French derivatives of Latin: Latin 'suavis' ("sweet") -> Vulgar/late-Latin verbal formations (e.g. *suavizare) -> Old French 'assouagier' / 'asoagier' -> Middle English forms (related to 'assuage') -> modern English adjective 'assuasive'.

Initially tied to the notion of 'making pleasant' or 'sweetening', the sense shifted toward 'lessening, soothing, or reducing intensity', which is the modern meaning.