Nothing in beer but a plant (4)
I believe the answer is:
aloe
'a plant' is the definition.
(aloe is a kind of plant)
'nothing in beer' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'in' is an insertion indicator.
'beer' becomes 'ale' (I've seen this before**).
'o' put into 'ale' is 'ALOE'.
'but' acts as a link.
(Other definitions for aloe that I've seen before include "Bitter drug from a leaf juice" , "shrub" , "Succulent plant (may be bitter!)" , "Bitter fruit" , "Succulent plant (4) 5532" .)