Nothing in beer plant (4)
I believe the answer is:
aloe
'plant' is the definition.
The answer is an example.
'nothing in beer' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'in' is an insertion indicator.
'beer' becomes 'ale' (type of beer).
'o' placed inside 'ale' is 'ALOE'.
(Other definitions for aloe that I've seen before include "O, ale with bitter plant" , "Genus of bitter herbs" , "Bitter drug from a leaf juice" , "Bitter fruit" , "Succulent plant (4) 5532" .)