(geometry) The locus of a point on the circumference of a circle that rolls without slipping on a fixed straight line. / (zoology) A fish having cycloid scales.

Resembling a circle; cycloidal. / (zoology, of fish scales) Thin and rounded, with smooth edges. / (psychoanalysis) characterized by alternating high and low moods.

(in the broad sense) a rapidly rotating storm system characterized by a low-pressure center, strong winds, and a circular/spiral arrangement of thunderstorms that produce heavy rain, ranging in increasing strength from tropical depressions and tropical storm to hurricanes.

(biochemistry) any of a class of cyclic oligomers of glucose; they have a toroidal shape and bind tightly with many aromatic compounds, the guest molecule fitting into the cavity like a key and lock; they mimic the action of several enzymes

(organic chemistry) An addition reaction that leads to the formation of a cyclic product.

An early particle accelerator in which charged particles were generated at a central source and accelerated spirally outward through a fixed magnetic field and alternating electric fields.

(organic chemistry) Any saturated alicyclic hydrocarbon.

Alternative spelling of cyclopaedia

(cycling) A device that counts the revolutions of a bicycle wheel in order to indicate distance travelled. / An instrument for measuring circular arcs.

(US) a domestic underground shelter used as protection from severe winds