'assister' originates from Latin, specifically the verb 'assistere,' where the prefix 'ad-' (assimilated to 'as-') meant 'to, toward' and 'sistere' meant 'to stand' or 'cause to stand.'

'assistere' passed into Old French as 'assister' meaning 'to stand by, help,' then into Middle English as 'assisten/assiste' and later developed into the modern English verb 'assist' and the agent noun 'assister.'

Initially it carried the sense 'to stand by' or 'be present'; over time the emphasis shifted to 'help, give support,' which is the dominant modern meaning.