trochoid
/ˈtrəʊkɔɪd
/adjective
1 Anatomy Denoting a joint in which one element rotates on its own axis (e.g. the atlas vertebra).The trochoid joint is composed of a ball shape that is surrounded by a circle composed of bone and ligaments....
- The third, a median joint formed by the dens of the axis and the fovea dentis of the atlas, is classified as a trochoid joint and permits rotation.
- It was in fact a spiral trochoid joint with a cuneiform convexity in all the simian primates except for the humans.
2 Geometry Denoting a curve traced by a point on a radius of a circle rotating along a straight line or another circle (a cycloid, epicycloid, or hypocycloid).The trochoid form that is attributed to ocean waves changes shape as the amplitude increases for a given wavelength....
- A trochoid curve is very similar to a cycloid curve.
- A trochoid curve is created by tracing the path of a point that is a distance b from the centre of the circle.
3 Zoology Having or denoting a form of mollusc shell which is conical with a flat base, like a top shell.The second corallum is a much larger, rounded trochoid form that approaches 11 cm in length and reached a maximum diameter of 4.7 cm....
- Thus, calice size may have been a factor (as discussed below), along with having a larger area for distribution of weight, which may account for the abundance of trochoid and patellate shapes in H. halli living on and in soft mud.
- The shell of Microdoma conicum bears an inner nacreous layer and their shell layers resemble those of modern trochoids.
noun
1A trochoid curve.Not only does the new one squeeze out the juice, it does so smoothly and quietly due to the nature of its two spinning, triangular trochoids, rather than the action of pumping pistons....
- A trochoid refers to any of the cycloid, the curtate cycloid and the prolate cycloid.
- It will be observed that when k=0, the hypertrochoid degenerates into a curtate hypotrochoid, but this degeneration keeps the curve in the set of hypertrochoids that contains the subset of trochoids.
2A trochoid joint.However, neontological evidence suggests that fissurelloids diverged from other vetigastropods relatively recently (e.g., after the divergence of trochoids, which likely was in the late Paleozoic).
Derivatives
trochoidal
- The siltstones are intensely rippled, with bedding planes showing original bedforms with straight crests, and symmetrical and trochoidal cross-sectional geometries; features typical of wave generated ripples.
- The engine housing 38 has an internal trochoidal surface TS typically found in rotary type engines.
- The notion ‘bearing reducers’ indicates the full integration of a high precision trochoidal reduction gear and a radial-axial bearing in a single unit.
Origin
Early 18th century: from Greek trokhoeidēs 'wheel-like', from trokhos 'wheel'.