hub

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The center part of a wheel, fan, or propeller.
• noun A center of activity or interest; a focal point.

from The Century Dictionary.

• noun A lump; a ridge; a small mass; any rough protuberance or projection. as, a hub in the road.
• noun A small stack of hay.
• noun A thick square sod pared off the surface of a peat-bog when digging for peat.
• noun A block of wood for stopping a carriage-wheel.
• noun In die-sinking, a cylindrical piece of steel on which the design for a coin is engraved in relief.
• noun A fluted screw of hardened steel, adapted to be placed on a mandrel between the centers of a lathe, notched to present cutting edges, and used in cutting screw-tools, chasing-tools, etc.
• noun In plumbing, a short piece of pipe with a bell at each end, used for joining pipes in line or at an angle. When one end is smaller than the other, to form a reducing-joint, it is a reduced hub.
• noun The wooden or metal center of a carriage-or wagon-wheel, into which the spokes are inserted; the nave.
• noun Something resembling the hub of a wheel in central position or importance.
• noun A mark at which quoits, etc., are cast.
• noun The hilt of a weapon.
• noun Also hob in some uses.

from the GNU version of the Collaborative International Dictionary of English.

• noun The central part, usually cylindrical, of a wheel; the nave. See Illust. of axle box.
• noun The hilt of a weapon.
• noun A rough protuberance or projecting obstruction. [U.S.] See Hubby.
• noun A goal or mark at which quoits, etc., are cast.
• noun (Diesinking) A hardened, engraved steel punch for impressing a device upon a die, used in coining, etc.
• noun A screw hob. See Hob, 3.
• noun A block for scotching a wheel.
• noun The central location within which activities tend to concentrate, or from which activities radiate outward; a focus of activity.
• noun (Aeronautics) A large airport used as a central transfer station for an airline, permitting economic air transportation between remote locations by directing travellers through the hub, often changing planes at the hub, and thus keeping the seat occupancy rate on the airplanes high. The hub together with the feeder lines from remote locations constitute the so-called hub and spoke system of commercial air passenger transportation. A commercial airline may have more than one such hub.
• noun The city of Boston, Massachusetts referred to locally by the nickname The Hub.
• noun (Highway Bridges) a horizontal guard plank along a truss at the height of a wagon-wheel hub.
• noun [Colloq.] as far as possible in embarrassment or difficulty, or in business, like a wheel sunk in mire; deeply involved.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The central part, usually cylindrical, of a wheel; the nave
• noun A point where many routes meet and traffic is distributed, dispensed or diverted
• noun computing a computer networking device connecting several ethernet ports. See switch.
• noun surveying A stake with a nail in it, used to mark a temporary point.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the central part of a car wheel (or fan or propeller etc) through which the shaft or axle passes
• noun a center of activity or interest or commerce or transportation; a focal point around which events revolve