late Middle English: from Old French, or from medieval Latin influentia ‘inflow’, from Latin influere, from in- ‘into’ + fluere ‘to flow’. The word originally had the general sense ‘an influx, flowing matter’, also specifically (in astrology) ‘the flowing in of ethereal fluid (affecting human destiny)’. The sense ‘imperceptible or indirect action exerted to cause changes’ was established in Scholastic Latin by the 13th century, but not recorded in English until the late 16th century.