'appulse' originates from Latin, specifically the past-participial form 'appulsus', where the prefix 'ad-' (later assimilated to 'ap-') meant 'to, toward' and the root related to 'pellere' meant 'to push or drive'.

'appulsus' passed into Late/Medieval Latin and New Latin as a technical term and was borrowed into English (chiefly in astronomical usage) as 'appulse' in the modern period; the English plural form became 'appulses'.

Initially it referred generally to a 'pushing to' or 'bringing to' (physical contact or approach); over time it specialized in astronomical contexts to mean a close apparent approach of one celestial body to another, while an older sense of 'bringing into contact' remains archaic.