bossn.[OE. boce, bose, boche, OF. boce, boche, bosse, F. bosse, of G. origin; cf. OHG. bzo tuft, bunch, OHG. bzan, MHG. bzen, to beat. See Beat, and cf. Botch a swelling.]1. Any protuberant part; a round, swelling part or body; a knoblike process; as, a boss of wood.()2. A protuberant ornament on any work, either of different material from that of the work or of the same, as upon a buckler or bridle; a stud; a knob; the central projection of a shield. See Umbilicus.()()3. (Arch.) A projecting ornament placed at the intersection of the ribs of ceilings, whether vaulted or flat, and in other situations.()[Cf. D. bus box, Dan. bsse.]4. A wooden vessel for the mortar used in tiling or masonry, hung by a hook from the laths, or from the rounds of a ladder.(Gwilt.)5. (Mech.) The enlarged part of a shaft, on which a wheel is keyed, or at the end, where it is coupled to another.()6. A head or reservoir of water.()v. t.[OE. bocen, fr. OF. bocier. See the preceding word.] To ornament with bosses; to stud.()n.[D. baas master.] A master workman or superintendent; a director or manager; a political dictator.()