trochoid

A curve traced by a point on or connected with a circle as the circle rolls along a fixed straight line.

Capable of or exhibiting rotation about a central axis.

Permitting rotation, as a pulley or pivot.

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.

In geometry, trochoidal.

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.

In conchology, top-shaped, like a shell of the genus Trochus; conical with a flat base; of or related to the Trochidæ.

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.

In anatomy, a rotatory or pivotal joint; diarthrosis rotatorius; cyclarthrosis.

In conchology, a top-shell, or some similar shell; any member of the Trochidæ.