Record one copyright for reason (5)
I believe the answer is:
logic
'reason' is the definition.
(I've seen this before)
'record one copyright' is the wordplay.
'record' becomes 'log' (logging is a kind of recording).
'one' becomes 'I' (Roman numeral).
'copyright' becomes 'C' (as in the copyright symbol, a C in a circle).
'log'+'i'+'c'='LOGIC'
'for' acts as a link.
(Other definitions for logic that I've seen before include "Science of correct reasoning" , "Sound reasoning" , "Chain of reasoning" , "Reasoned thinking" , "Reasoned argument" .)