Definify.com

Webster 1913 Edition

Sworn brothers

originally, companions in arms who took an oath to share together good and bad fortune; hence, faithful friends.

–

Sworn enemies

determined or irreconcilable enemies.

–

Sworn friends

close friends.

pp.

of swear. The officers of government are sworn to a faithful discharge of their duty.

Sworn friends, is a phrase equivalent to determined, close or firm friends.

I am sworn brother, sweet,

To grim necessity.

Sworn enemies, are determined or irreconcilable enemies.