Leaves much to be desired by abstainers (3)
I believe the answer is:
tea
'leaves' is the definition.
(as in tea leaves)
'much to be desired by abstainers' is the wordplay.
'much' means to remove the last letter (much but not all of the word).
'be desired by abstainers' becomes 'ea' (I am not sure about this - if you are sure you should believe this answer much more).
'to' with its last letter taken away is 't'.
't'+'ea'='TEA'
Can you help me to learn more?
(Other definitions for tea that I've seen before include "Afternoon or evening meal" , "Beverage from leaves" , "Perhaps Indian" , "Afternoon meal (3)" , "Dried leaf infusion" .)