BOSS

n. 1 a round knob, stud, or other protuberance, esp. on the centre of a shield or in ornamental work. 2 Archit. a piece of ornamental carving etc. covering the point where the ribs in a vault or ceiling cross. 3 Geol. a large mass of igneous rock. 4 Mech. an enlarged part of a shaft. [ME f. OF boce f. Rmc]