It relates to reason for employing casual (6)
I believe the answer is:
causal
'it relates to reason for' is the definition.
The definition suggests a singular noun but the answer is not.
'casual' is the wordplay.
'casual' can be anagrammed to 'CAUSAL'.
Though, I'm unsure how this is indicated.
'employing' acts as a link.
Can you help me to learn more?
(Other definitions for causal that I've seen before include "Producing an action" , "Producing an effect" .)