Green plan, green practice (10)
I believe the answer is:
chartreuse
'green' is the definition.
(I know that chartreuse is a type of green)
'plan green practice' is the wordplay.
'plan' becomes 'chart' (chart can mean a plan or diagram).
'green practice' becomes 'reuse' (I can't justify this - if you can you should give a lot more credence to this answer).
'chart'+'reuse'='CHARTREUSE'
Can you help me to learn more?
(Other definitions for chartreuse that I've seen before include "Green-yellow liqueur" , "green liquid" , "Green or yellow liqueur made by monks" , "Pale green-yellow colour" , "drink" .)