'assuager' originates from Latin, specifically from the Vulgar/late Latin element 'adsuaviare' (from ad- + suavis), where 'ad-' meant 'to/toward' and 'suavis' meant 'sweet' or 'pleasant'.

'assuager' came into English via Old French (Old French assouagier/assouagance) and Middle English 'assuagen' from Latin 'adsuaviare' and the adjective 'suavis', eventually forming the modern English verb 'assuage' and the agent noun 'assuager'.

Initially it carried the sense 'to make sweet or soften'; over time it evolved into the meaning 'to lessen, relieve, or ease (pain, grief, anger, etc.)', which is reflected in the agent noun 'assuager' as 'one who eases or relieves'.