Trochoid
Century Dictionary and Cyclopedia

 n trochoid In geometry: The curve described by any point on a radius of the rolling circle, or on a radius produced when two circles are tangent either externally or internally and, while one of them remains fixed, the other rolls upon it without sliding.
 trochoid In geometry, trochoidal.
 trochoid In anatomy, rotating or revolving like a wheel; pivotal, as an articulation; trochoidal: applied to that kind of rotatory arthrosis in which a part revolves to some extent upon another, as the head of the radius in the lesser sigmoid cavity of the ulna in pronation and supination of the forearm, or the atlas about the odontoid process of the axis in shaking the head.
 trochoid In conchology, topshaped, like a shell of the genus Trochus; conical with a flat base; of or related to the Trochidæ.
 n trochoid In geometry, a prolate or curtate cycloid or curve traced by a point in fixed connection with, but not generally on the circumference of, a wheel which rolls upon a right line. If the point is outside the circumference, the trochoid has loops; if inside, it has waves. See cycloid.
 n trochoid In anatomy, a rotatory or pivotal joint; diarthrosis rotatorius; cyclarthrosis.
 n trochoid In conchology, a topshell, or some similar shell; any member of the Trochidæ.
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Chambers's Twentieth Century Dictionary

 n Trochoid trō′koid the curve traced by a fixed point in a wheel which rolls in a right line
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Webster's Revised Unabridged Dictionary
Gr. a wheel + oid,; cf. F. trochoïde,. See Troche
Chambers's Twentieth Century Dictionary
Gr. trochæidēs, round like a wheel—trochos, wheel, eidos, form.
In literature:
Then any point in the circumference of the halfcrown will move through a curve called a 'trochoid.
"Boating" by W. B. Woodgate
For epi and hypocycloids and epi and hypotrochoids see EPICYCLOID.
"Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 8" by Various
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