'Sworn friends' definitions:

Definition of 'Sworn friends'

From: GCIDE

Sworn \Sworn\, p. p. of Swear. [1913 Webster]
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. [1913 Webster]