'appeasableness' originates from English formation based on the verb 'appease' (Middle English 'appesen'), ultimately from Old French 'apaisier/apaiser', where the element 'pais'/'paix' (from Latin 'pax, pac-') meant 'peace'.

'appease' changed from Old French 'apaisier' (apaiser) and entered Middle English as 'appesen'/'appeasen'; the adjective 'appeasable' was formed by adding the suffix '-able', and the noun-forming suffix '-ness' produced 'appeasableness'.

Initially the root meant 'make peaceful' or 'bring peace'; over time derivatives came to denote the capacity or quality of being made peaceful or calmed — hence 'appeasableness' meaning 'capability of being appeased'.