[ sahy-kloid ]

  1. resembling a circle; circular.

  2. (of the scale of a fish) smooth-edged, more or less circular in form, and having concentric striations.

  1. (of a fish) having such scales.

  2. Psychiatry. of or noting a personality type characterized by wide fluctuation in mood within the normal range.

  1. a cycloid fish.

  2. Geometry. a curve generated by a point on the circumference of a circle that rolls, without slipping, on a straight line.

Origin of cycloid

First recorded in 1655–65, cycloid is from the Greek word kykloeidḗs like a circle. See cycl-, -oid

Other words from cycloid

  • cy·cloi·dal, adjective
  • cy·cloi·dal·ly, adverb

Words Nearby cycloid Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use cycloid in a sentence

British Dictionary definitions for cycloid


/ (ˈsaɪklɔɪd) /

  1. resembling a circle

  2. (of fish scales) rounded, thin, and smooth-edged, as those of the salmon

  1. psychiatry (of a type of personality) characterized by exaggerated swings of mood between elation and depression: See also cyclothymia

  1. geometry the curve described by a point on the circumference of a circle as the circle rolls along a straight line: Compare trochoid (def. 1)

  2. a fish that has cycloid scales

Derived forms of cycloid

  • cycloidal, adjective
  • cycloidally, adverb

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for cycloid


[ kloid′ ]

  1. Resembling a circle.

  2. Thin, rounded, and smooth-edged, like a disk. Used of fish scales.

  1. The curve traced by a point on the circumference of a circle that rolls on a straight line.

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.