Command a fraternity of knights (5)
I believe the answer is:
order
I believe this clue is a double definition.
'command' is the first definition.
(I know that order is a type of command)
'a fraternity of knights' is the second definition.
(I've seen this in another clue)
(Other definitions for order that I've seen before include "rule of law" , "Command; arrange" , "One may be tall if demanding" , "An authoritative command" , "in which things are properly arranged?" .)