A circle, circular movement, or regular repetition.
[Either Greek kuklos, circle, or English cycle or cyclic.]
Words that include the idea of a circle include cyclorama, originally a large cylindrical picture designed to be viewed from inside, today usually a curved backdrop in a theatre, and cyclostome, an eel-like animal with a circular sucking mouth, such as a lamprey.
Other examples suggest circular movement: a cycloid is a curve marked out by a point on a circle rolling along a straight line, such as a point on a moving vehicle wheel; a cyclotron is a circular device for accelerating atomic and subatomic particles. A few compounds refer to a cyclic recurring condition, as in cyclothymia, a mental state in which the sufferer swings repeatedly between depression and elation.
In chemistry, the form marks a compound that contains a closed chain or ring of carbon atoms, as in cyclohexane, a colourless liquid used as a paint solvent. In medicine, cyclosporin (Greek spora, spore), a cyclic peptide derived from a fungus, is used to prevent rejection of grafts.