Pronunciation: (sī'kloid),[key] —adj. 1. resembling a circle; circular.
2. (of the scale of a fish) smooth-edged, more or less circular in form, and having concentric striations.
3. (of a fish) having such scales.
4. Psychiatry.of or noting a personality type characterized by wide fluctuation in mood within the normal range.
—n. 1. a cycloid fish.
2. Geom.a curve generated by a point on the circumference of a circle that rolls, without slipping, on a straight line.