n. The wider part or belly of a cask, which is usually in the middle.n. The breadth of a ship's bottom, or that part of her floor which approaches a horizontal direction, and on which she would rest if aground.Nautical, to suffer a fracture in the bilge; spring a leak by a fracture in the bilge.To bulge or swell out.To break or stave in (the bilge or bottom of a ship).