Cy"cloid (s?"kloid), *n.* [*Cyclo-
* + *-oid*: cf. F. *cycloïde*.] *(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.

&fist; 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.* *(Zoöl.)*
Of or pertaining to the Cycloidei.

**Cycloid scale***(Zoöl.)*,

a
fish scale which is thin and shows concentric lines of growth,
without serrations on the margin.Cy"cloid, *n.* *(Zoöl.)*
One of the Cycloidei.