[ sahy-kloid ]
/ ˈsaɪ klɔɪd /


resembling a circle; circular.
(of the scale of a fish) smooth-edged, more or less circular in form, and having concentric striations.
(of a fish) having such scales.
Psychiatry. of or noting a personality type characterized by wide fluctuation in mood within the normal range.


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

Nearby words

  1. cyclohexane,
  2. cyclohexanone,
  3. cycloheximide,
  4. cyclohexylamine,
  5. cyclohexylsulfamic acid,
  6. cycloidal propulsion,
  7. cyclolysis,
  8. cyclometer,
  9. cyclometric,
  10. cyclonal

Origin of cycloid

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

Related formscy·cloi·dal, adjectivecy·cloi·dal·ly, adverb Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for cycloid

British Dictionary definitions for cycloid


/ (ˈsaɪklɔɪd) /


resembling a circle
(of fish scales) rounded, thin, and smooth-edged, as those of the salmon
psychiatry (of a type of personality) characterized by exaggerated swings of mood between elation and depressionSee also cyclothymia


geometry the curve described by a point on the circumference of a circle as the circle rolls along a straight lineCompare trochoid (def. 1)
a fish that has cycloid scales
Derived Formscycloidal, adjectivecycloidally, 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

Science definitions for cycloid


[ sīkloid′ ]

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