| any of the long, cylindrical, marrow-containing bones of the limbs: the long bone of the arm. |

| long bone n. Any of several elongated bones of vertebrate limbs that have a roughly cylindrical shaft containing marrow. |
long bone n.
One of the elongated bones of the extremities, consisting of a tubular shaft, which is composed of compact bone surrounding a central marrow-filled cavity, and two expanded portions that usually serve as articulation points.