a. A protuberance or swelling on the body of an animal or plant; a convex or knob-like process or excrescent portion of an organ or structure; in 16th cent. applied to the lobe of the liver, spleen, etc.; as now used it seems partly transferred from 3.

†b. spec. A hump or hunch on the back. Obsolete.

†c. A protuberance made by padding the dress. Obsolete.

†d. The big bulk of an animal; a bulky animal.

†e. A fat woman. Obsolete.

a. A round prominence in hammered or carved work, etc.; e.g. a raised ornament in bookbinding (in earlier use, esp. the ‘umbo’ or round knob, often of precious metal, which occupied the centre of the cover); one of the metal knobs on each side of the bit of a bridle (French bossette); a metal stud used for ornament. †in boss: in high relief; cf. French en bosse.

b. spec. The convex projection in the centre of a shield or buckler.

c. transferred and figurative.

†d. = bossell n. Obsolete. rare.

e. Architecture. An ornamental projection in a vault at the intersection of the ribs.

f. Mechanics. ‘The enlarged part of a shaft, on which a wheel is keyed, or at the end, where it is coupled to another’ (Webster). Shipbuilding. The projecting part of the stern-post of a screw steamer, which is pierced for the shaft of the propeller to pass through. (Cf. French bosse nave of a wheel.)

g. A soft pad used in ceramics and glass-manufacture for smoothing and making uniform the colours applied with oil to a glass or porcelain surface, and for cleaning gilded surfaces.

h. (See quot.)

i. The central portion of the propeller of an aeroplane.

a. transitive. To make to project, to stuff out. Obsolete.

†b. intransitive. To swell out, project. Obsolete.

a. transitive. To fashion in relief; to beat or press out into a raised ornament, to emboss.

b. In ceramics, to smooth a surface of boiled oil on pottery by means of a boss (boss n.¹ 3g).