early 15c., "eccentric circle or orbit," originally a term in Ptolemaic astronomy, "circle or orbit not having the Earth precisely at its center," from French eccentrique and directly from Medieval Latin eccentricus (noun and adjective), from Greek ekkentros "out of the center" (as opposed to concentric), from ek "out" (see ex-) + kentron "center" (see center (n.)). Meaning "odd or whimsical person" is attested by 1817 (S.W. Ryley, "The Itinerant, or Memoirs of an Actor").
June 4 .—Died in the streets in Newcastle, William Barron, an eccentric, well known for many years by the name of Billy Pea-pudding. [John Sykes, "Local Records, or Historical Register of Remarkable Events which have Occurred Exclusively in the Counties of Durham and Northumberland, Town and County of Newcastle Upon Tyne, and Berwick Upon Tweed," Newcastle, 1824]
1550s, from French eccentrique and directly from Medieval Latin eccentricus (noun and adjective; see eccentric (n.)). Of persons, figurative sense of "odd, whimsical" first recorded 1620s. "Eccentric is applied to acts which are the effects of tastes, prejudices, judgments, etc., not merely different from those of ordinary people, but largely unaccountable and often irregular ..." [Century Dictionary].