The deepest or lowest part: the bottom of a well; the bottom of the page. The part closest to a reference point: was positioned at the bottom of the key for a rebound. The underside: scraped the bottom of the car on a rock. The supporting part; the base. The far end or part: at the bottom of the bed. The last place, as on a list. The lowest or least favorable position: started at the bottom of the corporate hierarchy. The basic underlying quality; the source: Let's get to the bottom of the problem. The solid surface under a body of water. Low-lying alluvial land adjacent to a river. Often used in the plural. Also called bottomland. Nautical The part of a ship's hull below the water line. A ship; a boat: "English merchants did much of their overseas trade in foreign bottoms\u201d ( G.M. Trevelyan). The trousers or short pants of pajamas. Often used in the plural. Informal The buttocks. The seat of a chair. Baseball The second or last half of an inning. Staying power; stamina. Used of a horse. To provide with an underside. To provide with a foundation. To get to the bottom of; fathom. To be or become based or grounded. To rest on or touch the bottom. bottom out To descend to the lowest point possible, after which only a rise may occur: Sales of personal computers have bottomed out. at bottom Basically.