Dram from non-drinker getting round in (3)
I believe the answer is:
tot
'dram' is the definition.
(I've seen this before)
'non-drinker getting round in' is the wordplay.
'non drinker' becomes 'tt' (Teetotaller abbreviation).
'getting round' becomes 'o' (I've seen this in other clues).
'in' is an insertion indicator.
'tt' placed around 'o' is 'TOT'.
'from' acts as a link.
(Other definitions for tot that I've seen before include "Add a small drink of rum for the toddler" , "A wee dram" , "quick drink" , "nipper" , "Small quantity of alcoholic drink" .)