'appropinquation' originates from Latin, specifically the word 'appropinquatio' (from the verb 'appropinquare'), where 'ad-' (ap-) meant 'to' and 'propinquus' meant 'near'.

'appropinquation' entered English from Medieval/Neo-Latin 'appropinquatio' (or from the verb 'appropinquare') and was used in Early Modern English with the sense of 'a drawing near' or 'approach'.

Initially it meant 'the act of drawing near' in a literal or figurative sense, and over time the basic sense of 'approach/nearness' has largely remained, though the noun has become rare/archaic in modern usage.