Source : Webster's Revised Unabridged Dictionary (1913)

Trochoid \Tro"choid\, n. [Gr. ? a wheel + -oid; cf. F.
   trocho["i]de. See {Troche}.] (Geom.)
   The curve described by any point in a wheel rolling on a
   line; a cycloid; a roulette; in general, the curve described
   by any point fixedly connected with a moving curve while the
   moving curve rolls without slipping on a second fixed curve,
   the curves all being in one plane. Cycloids, epicycloids,
   hypocycloids, cardioids, etc., are all trochoids.

Trochoid \Tro"choid\, a.
   1. (Anat.) Admitting of rotation on an axis; -- sometimes
      applied to a pivot joint like that between the atlas and
      axis in the vertebral column.

   2. (Zo["o]l.) Top-shaped; having a flat base and conical
      spire; -- said of certain shells.

   3. (Zo["o]l.) Of or pertaining to the genus Trochus or family
      {Trochid[ae]}.