trochoid

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A curve traced by a point on or connected with a circle as the circle rolls along a fixed straight line.
• adjective Capable of or exhibiting rotation about a central axis.
• adjective Permitting rotation, as a pulley or pivot.

from The Century Dictionary.

• noun 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.
• noun 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.
• noun In anatomy, a rotatory or pivotal joint; diarthrosis rotatorius; cyclarthrosis.
• noun In conchology, a top-shell, or some similar shell; any member of the Trochidæ.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Geom.) The curve described by any point in a wheel rolling on a line; a cycloid; a roulette; in general, the curve described by any point fixedly connected with a moving curve while the moving curve rolls without slipping on a second fixed curve, the curves all being in one plane. Cycloids, epicycloids, hypocycloids, cardioids, etc., are all trochoids.
• adjective (Anat.) Admitting of rotation on an axis; -- sometimes applied to a pivot joint like that between the atlas and axis in the vertebral column.
• adjective (Zoöl.) Top-shaped; having a flat base and conical spire; -- said of certain shells.
• adjective (Zoöl.) Of or pertaining to the genus Trochus or family Trochidæ.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun mathematics The curve traced by a point on a circle as it rolls along a straight line
• adjective capable of rolling
• adjective allowing rotation