Punishment about it is limited (6)
I believe the answer is:
finite
'is limited' is the definition.
(similar in meaning)
'punishment about it' is the wordplay.
'punishment' becomes 'fine' (fine is a kind of punishment).
'about' indicates putting letters inside.
'fine' enclosing 'it' is 'FINITE'.
(Other definitions for finite that I've seen before include "Bounded or limited" , "Bounded or measurable" , "Bounded in time" , "Restricted - having limits" , "Limited in extent" .)