epicycloid
[epuhsahykloid]

noun Geometry.
a curve generated by the motion of a point on the circumference of a circle that rolls externally, without slipping, on a fixed circle. Equation: x = (a + b) cos(θ) − b cos[(a + b)θ/b] and y = (a + b) sin(θ) − b sin[(a + b)θ/b].
Compare epitrochoid.
Origin of epicycloid
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Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
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Historical Examples of epicycloid
It follows that a line from B to M will always be tangential to the epicycloid.
Suppose b a tracing point on b, then as b rolls on a it will describe the epicycloid a b.
It is impossible to mill out even a convex cycloid or epicycloid, by the means and in the manner above described.
But if a circle be made to roll along the circumference of another circle, it becomes an epicycloid (which see).
The Sailor's WordBookWilliam Henry Smyth
The epicycloid shown is termed the “threecusped epicycloid” or the “epicycloid of Cremona.”
epicycloid
noun
Collins English Dictionary  Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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epicycloid
[ĕp′ĭsī′kloid′]
The American Heritage® Science Dictionary
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