Note: in AM, use 'double-barreled'
1.
A ~ gun has two barrels.
...a ~ shotgun.
ADJ: ADJ n
2.
A ~ surname has two parts which are joined by a hyphen, for example ‘Miss J. Heydon-Smith’. (BRIT)
ADJ: ADJ n
3.
Double-barrelled is used to describe something such as a plan which has two main parts. (JOURNALISM)
ADJ: ADJ n