Replace drink with vegetable (8)
I believe the answer is:
supplant
'replace' is the definition.
(I know that replace can be written as supplant)
'drink with vegetable' is the wordplay.
'drink' becomes 'sup' (to sup is to drink).
'with vegetable' becomes 'plant' (I can't justify this - if you can you should give a lot more credence to this answer).
'sup'+'plant'='SUPPLANT'
Can you help me to learn more?
(Other definitions for supplant that I've seen before include "Supersede and replace" , "Oust" , "Displace" , "take another's place" .)