The Collaborative International Dictionary
Sworn brothers
Sworn \Sworn\, p. p. of Swear.
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.
Wikipedia
Sworn Brothers
Sworn Brothers is a 1987 Hong Kong action crime drama film directed by David Lai and starring Andy Lau and Cheung Kwok-keung as step brothers on the opposite sides of the law as a triad and cop respectively.