Barrel

[1] A hollow, usually cylindrical, machine part, often revolving, sometimes with wall apertures
[2] The air horn in the carburetor. In particular, it is that part where the throttle valve is located. If a carburetor has four openings with a throttle valve in each, it is called a "four-barrel carburetor".
See also carburetor barrel, four barrel carburetor, four barrel
[3] Another name for the carburetor barrel, cylinder, cylinder barrel, four barrel, polishing barrel, and single barrel.
[4] To travel fast as in We barrelled down the highway well above the speed limit.
[5] The main cylinder in which molten polymer is prepared for extrusion or injection into molds. See injection molding
[6] (bbl) A capacity of 42 US gallons (35 imperial gallons or 159.1 liters) frequently used as a unit in the oil industry.