What is the meaning of Cubitus?

The ulna.

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.

The elbow, or the corresponding joint in the forelimb of a quadruped.

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.

ulna

reclined, lying down, having been reclined.

a lying down

bed, couch

Alternative form of cubitum

ulna

Source: wiktionary.org