Cycloid

n. [Fr. cycloïde, from Gr. κύκλος, circle, and εἶδος, form.] (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.

☞ The common cycloid is the curve described when the generating point 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 lies within that circumference. Math. Dict.

n. A fish of the fourth order, according to the arrangement of Agassiz, having membranous scales, without teeth, or spines, on the margins, as the herring and salmon.

a. Belonging to the cycloidians.