rare The patella (kneecap).
historical A mechanical device showing the motion of the sun and moon and their position for each day of the year. More fully "astronomical rotula".
A keyhole urchin or sand dollar of the West African genus Rotula (order Clypeasteroida), having a round, flattened test with deep notches along the edge. Also (in form Rotula): the genus itself.
4Each of five radial elements forming part of the oral apparatus (Aristotle's lantern) of echinoids.
5rare A circular structure forming the end of some sponge spicules; = "rotule". Also: a wheel-shaped spicule in the integument of certain holothurians.
Late Middle English; earliest use found in Lanfranc's Science of Cirurgie. From classical Latin rotula small wheel, in post-classical Latin also kneecap from rota wheel + -ula.