trochoid

Concise Oxford English Dictionary © 2008 Oxford University Press:
trochoid /ˈtrəʊkɔɪd/

▶adjective

• 1 Anatomy denoting a joint in which one element rotates on its own axis (e.g. the atlas vertebra).

• 2 Geometry denoting a curve traced by a point on a radius of a circle rotating along a straight line or another circle.

• 3 Zoology (of a mollusc shell) conical with a flat base.

▶noun

• 1 a trochoid curve.

• 2 a trochoid joint.

– derivatives
trochoidal adjective.

– origin C18: from Gk trokhoeidēs ‘wheel-like’, from trokhos ‘wheel’.