For set, Fay arranged security (6)
I believe the answer is:
safety
'security' is the definition.
(being secure is being safe)
'for set fay arranged' is the wordplay.
'set fay' anagrams to 'SAFETY'.
But, I'm not clear how this is indicated.
Can you help me to learn more?
(Other definitions for safety that I've seen before include "Motto of the cautious!" , "State of security" , "Security; sanctuary" , "The condition of being protected from danger" , "Sort of catch" .)