Punishing plane perhaps (5)
I believe the answer is:
penal
'punishing' is the definition.
(I've seen this before)
'plane perhaps' is the wordplay.
'perhaps' indicates anagramming the letters.
'plane' with letters rearranged gives 'PENAL'.
(Other definitions for penal that I've seen before include "Corrective" , "Involving legal punishment" , "Very severe" , "Punishing" , "Relating to legal punishment" .)