Full Definition of BARN. 1. a: a usually large building for the storage of farm products or feed and usually for the housing of farm animals or farm equipment. 2. : a large building for the housing of a fleet of vehicles (as trolley cars or trucks).— barn·like \-ˌlīk\ adjective.arn. noun \ˈbaern\. : ˈbärn a building used for storing grain and hay and for housing farm. animals \noun\. ˈbaern ˈbärn