said of an anatomical joint: having one part that moves round a central axis to allow rotational movement, e.g. the joint between the vertebrae at the top of the neck
said of a curve in geometry: following a path generated by a point on the radius of a circle as the circle rolls on a fixed straight line
said of the shell of certain molluscs: conical with a flat base
trochoidal /trohʹkoydl/ adj
[Greek trokhoeidēs like a wheel, from trokhos a wheel]