'appulse' originates from Latin, specifically the past participle form 'appulsus' (from ad- + pulsus), where 'ad-' meant 'toward' and 'pulsus' (from pellere/pulsare) meant 'driven' or 'pushed'.

'appulse' passed into Medieval and later scientific English from Medieval Latin 'appulsus' as a noun meaning a pushing-together or nearest approach; the adjective 'appulsive' and the adverb 'appulsively' were later derived in English to describe related properties or manners.

Initially it referred generally to a pushing or coming-together ('a driven/struck-together' sense); over time it acquired a technical sense of 'near approach' (notably in astronomy) and adjectival/adverbial senses derived from that.