Rod will be faithful (5)
I believe the answer is:
stick
'rod' is the definition.
(rod is a type of stick)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for stick that I've seen before include "Adhere - cane" , "Flak - cling" , "Switch < put up" , "Tolerate" , "Glue; piece of wood" .)