<p><strong>Adjective</strong></p><ul><li>resembling a circle; circular.</li><li>(of the scale of a fish) smooth-edged, more or less circular in form, and having concentric striations.</li><li>(of a fish) having such scales.</li><li>Psychiatry. of or noting a personality type characterized by wide fluctuation in mood within the normal range.</li></ul><p><strong>Noun</strong></p><ul><li>a cycloid fish.</li><li>Geometry. a curve generated by a point on the circumference of a circle that rolls, without slipping, on a straight line.</li></ul>