Give a justification for former patent (7)
I believe the answer is:
explain
'give a justification for' is the definition.
(explain can mean to justify)
'former patent' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'patent' becomes 'plain' (synonyms).
'ex'+'plain'='EXPLAIN'
(Other definitions for explain that I've seen before include "Elucidate, clarify" , "Elucidate, make clear" , "offer clarification" , "Show the meaning of, make clear" , "Defend" .)