It marks rank of crazy priest (6)
I believe the answer is:
stripe
'it marks rank' is the definition.
The definition suggests a singular noun which matches the answer.
'crazy priest' is the wordplay.
'crazy' indicates anagramming the letters.
'priest' is an anagram of 'STRIPE'.
'of' is the link.
Can you help me to learn more?
(Other definitions for stripe that I've seen before include "Length of material, maybe showing rank" , "Chevron indicating rank" , "Narrow band of colour" , "Military rank indicator" , "Military mark of rank, chevron" .)