\Cy"cloid\ (s?"kloid), n. [Cyclo- + -oid: cf. F.
cyclo["i]de.] (Geom.)
A curve generated by a point in the plane of a circle when
the circle is rolled along a straight line, keeping always in
the same plane.
Note: The common cycloid is the curve described when the
      generating point (p) is on the circumference of the
      generating circle; the curtate cycloid, when that point
      lies without the circumference; the prolate or
      inflected cycloid, when the generating point (p) lies
      within that circumference.

\Cy"cloid\, a. (Zo["o]l.)
Of or pertaining to the Cycloidei.
{Cycloid scale} (Zo["o]l.), a fish scale which is thin and
   shows concentric lines of growth, without serrations on
   the margin.

\Cy"cloid\, n. (Zo["o]l.)
One of the Cycloidei.