Cycloid \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.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Cycloid \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.

Source: Webster's Revised Unabridged Dictionary (1913)
 

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

Source: Webster's Revised Unabridged Dictionary (1913)