In getting a plant substance, commit another offence (5)
I believe the answer is:
resin
'in getting a plant substance commit' is the definition.
I can't judge whether this definition defines the answer.
'another offence' is the wordplay.
'another' becomes 're' (I've seen this in other clues).
'offence' becomes 'sin' (a sin is an offence or transgression).
're'+'sin'='RESIN'
Can you help me to learn more?
(Other definitions for resin that I've seen before include "Very important part of plastics industry" , "It exudes from pines" , "Cannabis, say" , "hashish, say" , "component of varnish" .)