Bar·rel 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.
 5. A jar. [Obs.]
 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.