epitrochoid

[ep-i-troh-koid]

Geometry.

a plane curve generated by the motion of a fixed point on the radius or extension of the radius of a circle that rolls externally, without slipping, on a fixed circle. The epitrochoid is a generalization of the epicycloid.

Origin of epitrochoid

First recorded in 1835–45; epi- + trochoid

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

The curve may be regarded as an epitrochoid (see Epicycloid) in which the rolling and fixed circles have equal radii.
Encyclopaedia Britannica, 11th Edition, Volume 16, Slice 6
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