c.1400, "of or like a ray or radius," from Medieval Latin radialis, from Latin radius "shaft, rod; spoke of a wheel; beam of light" (see radius). As a noun, a type of tire, attested from 1965, short for radial-ply (tire). Related: Radially.
radial ra·di·al (rā'dē-əl)
Of, relating to, or near the radius or forearm.
Moving or directed along a radius.
Radiating from or converging to a common center.