headern.1. One who, or that which, heads nails, rivets, etc., esp. a machine for heading.()2. One who heads a movement, a party, or a mob; head; chief; leader.()3. (Arch.) A brick or stone laid with its shorter face or head in the surface of the wall.()4. A reaper for wheat, that cuts off the heads only.()5. A fall or plunge head first, as while riding a bicycle, or a skateboard, or in bathing; -- sometimes, implying the striking of the head on the ground; as, to take a header.()adv. With the head foremost; -- of motion.()