eccentric

eccentric in mechanics, device for changing rotary to back-and-forth motion. A disk is mounted off center on a shaft. One flat, open, circular end of a rod fits around the edge of the disk; the other end is usually attached to a block that slides in a slot. As the shaft rotates the block slides back and forth, carrying along whatever is attached to it, e.g., a valve. The distance between the center of the shaft and the center of the disk is the eccentricity. The so-called throw may mean either the eccentricity or the distance the block moves, which is twice the eccentricity. Cams and cranks perform the same function as the eccentric, which designers often prefer to the crank for short motions.

ec·cen·tric / ikˈsentrik/ • adj. 1. (of a person or behavior) unconventional and slightly strange: my favorite aunt is very eccentric. 2. technical (of a thing) not placed centrally or not having its axis or other part placed centrally. ∎  (of a circle) not centered on the same point as another. ∎  (of an orbit) not circular. • n. 1. a person of unconventional and slightly strange views or behavior: he enjoys a colorful reputation as an engaging eccentric. 2. a disc or wheel mounted eccentrically on a revolving shaft in order to transform rotation into backward-and-forward motion, e.g., a cam in an internal combustion engine. DERIVATIVES: ec·cen·tri·cal·ly adv.

eccentric not concentric XVI (as sb. XV); not central or referable to a centre; irregular, odd XVII; sb. (person) XIX, after F. — late L. eccentricus, f. Gr. ékkentros, f. ek out, EX-2 + kéntron CENTRE; cf. (O)F. excentrique.
Hence eccentricity XVI.