Herb put nothing in beer (4)
I believe the answer is:
aloe
'herb' is the definition.
The answer and definition can be both plants as well as being singular nouns.
Maybe there's a link between them I don't understand?
'nothing in beer' is the wordplay.
'nothing' becomes 'o' (O resembles 0).
'in' means one lot of letters goes inside another.
'beer' becomes 'ale' (type of beer).
'o' inserted within 'ale' is 'ALOE'.
'put' is the link.
Can you help me to learn more?
(Other definitions for aloe that I've seen before include "Plant source of purgative drug" , "Genus of bitter herbs" , "Bitter drug from a leaf juice" , "has a bitter taste" , "Bitter fruit" .)