1. The brother of a husband or wife, or the husband of one's sister.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• vrother-in-law,
• nrother-in-law,
• hrother-in-law,
• grother-in-law,
• beother-in-law,
• bdother-in-law,
• bfother-in-law,
• btother-in-law,
• b5other-in-law,
• b4other-in-law,
• brither-in-law,
• brkther-in-law,
• brlther-in-law,
• brpther-in-law,
• br0ther-in-law,
• br9ther-in-law,
• brorher-in-law,
• brofher-in-law,
• brogher-in-law,
• broyher-in-law

The adjective form of "brother-in-law" is "brother-in-lawly". However, this is not a common or widely recognized word. In most cases, people would typically describe their brother-in-law using phrases or other adjectives to convey specific qualities or characteristics.