'appeasable' originates from English verb 'appease' (from Old French 'apaisier') combined with the adjectival suffix '-able' (from Latin '-abilis'), where 'apaisier' contained the root 'pais' meaning 'peace' and '-able' meant 'able to / capable of'.

'appease' changed from Old French 'apaisier' into Middle English 'appeasen' and eventually became the modern English verb 'appease'; the adjective 'appeasable' was formed from that verb plus the suffix '-able'.

Initially it meant 'to bring to peace; to make peaceful,' but over time it evolved to the current sense of 'to pacify or placate (someone) / to relieve (a feeling)'.