Influence
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.
wiktionary
From Middle English influence, from Old French influence(“emanation from the stars affecting one's fate”), from Medieval Latin īnfluentia, from Latin īnfluēns(“flowing in”), present active participle of īnfluō(“flow into”), from in-(“in-”) + fluō(“flow”). Doublet of influenza.
etymonline
influence (n.)
late 14c., an astrological term, "streaming ethereal power from the stars when in certain positions, acting upon character or destiny of men," from Old French influence "emanation from the stars that acts upon one's character and destiny" (13c.), also "a flow of water, a flowing in," from Medieval Latin influentia "a flowing in" (also used in the astrological sense), from Latin influentem (nominative influens), present participle of influere "to flow into, stream in, pour in," from in- "into, in, on, upon" (from PIE root *en "in") + fluere "to flow" (see fluent).
The range of senses in Middle English was non-personal, in reference to any outflowing of energy that produces effect, of fluid or vaporous substance as well as immaterial or unobservable forces. Meaning "exertion of unseen influence by persons" is from 1580s (a sense already in Medieval Latin, for instance Aquinas); meaning "capacity for producing effects by insensible or invisible means" is from 1650s. Under the influence (of alcohol, etc.) "drunk" first attested 1866.
influence (v.)
1650s, from influence (n.). Related: Influenced; influencing.
