'assuage' originates from Old French, specifically the word 'assouagier' (to soften or make pleasant), ultimately related to Latin roots including 'ad-' (toward) and 'suavis' (sweet, pleasant). 'assuagable' is formed in English by adding the adjectival suffix '-able' to 'assuage'.

'assuage' passed into Middle English from Old French 'assouagier' (and related Late Latin forms), later becoming modern English 'assuage'; the adjectival form 'assuagable' (also spelled 'assuageable') was formed by adding '-able' to mean 'able to be assuaged'.

Initially related to making something 'sweet' or 'pleasant' (from Latin 'suavis'), the sense shifted to 'soften' or 'lessen' suffering or severity; today it commonly means 'able to be eased or relieved'.