c.1374, an astrological term, "streaming ethereal power from the stars acting upon character or destiny of men," from O.Fr.
influence "emanation from the stars that acts upon one's character and destiny" (13c.), also "a flow of water," from M.L.
influentia "a flowing in" (also used in the astrological sense), from L.
influentem (nom.
influens), prp. of
influere "to flow into," from
in- "in" +
fluere "to flow" (see
fluent). Meaning "exercise of personal power by human beings" is from 1439; meaning "exertion of unseen influence by persons" is from 1588 (a sense already in M.L., e.g. Aquinas).
Under the influence "drunk" first attested 1866.
Influential "powerful" is from 1734.
[in-floo-uh
ns] 
noun, verb, -enced, -enc⋅ing.