Definition of "cubitus"

(archaic) The ulna.

(entomology) One of the major veins of the insect wing, between the media and the postcubitus; the vein running along the dorsal edge of the discal cell.

(anatomy) The elbow, or the corresponding joint in the forelimb of a quadruped.  examples

(anatomy) The forearm; the arm from the elbow to fingertip, or the corresponding portion of a jointed limb of an animal that uses the limb for locomotion or grasping.  examples