n. The act of lying or the state of being laid on the back, or face upward.n. In anatomy and physiology: A movement of the forearm and hand of man and some other animals which brings the palm of the hand uppermost and the radius and ulna parallel with each other, instead of crossing each other as in the opposite movement of pronation.n. The position of the forearm and hand in which the ulna and radius lie parallel, not crossed, and the hand lies flat on its back, palm upward: the opposite of pronation. The act is accomplished and the position is assumed by means of the supinators, aided by the biceps.n. In fencing, the position of the wrist when the palm of the hand is turned upward.