Barrel n. 1.A round vessel or cask, of greater length than breadth, and bulging in the middle, made of staves bound with hoops, and having flat ends or heads; as, a cracker barrel. Sometimes applied to a similar cylindrical container made of metal, usually called a drum.
2.The quantity which constitutes a full barrel. This varies for different articles and also in different places for the same article, being regulated by custom or by law. A barrel of wine is 31½ gallons; a barrel of flour is 196 pounds.
3.A solid drum, or a hollow cylinder or case; as, the barrel of a windlass; the barrel of a watch, within which the spring is coiled.
4.A metallic tube, as of a gun, from which a projectile is discharged.
6.(Zool.) The hollow basal part of a feather.
Barrel bulk (Com.), a measure equal to five cubic feet, used in estimating capacity, as of a vessel for freight.
Barrel drain (Arch.), a drain in the form of a cylindrical tube.
Barrel of a boiler, the cylindrical part of a boiler, containing the flues.
Barrel of the ear (Anat.), the tympanum, or tympanic cavity.
Barrel organ, an instrument for producing music by the action of a revolving cylinder.
Barrel vault. See under Vault. 
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