Note small amount drunk (5)
I believe the answer is:
minim
'note' is the definition.
(type of musical note)
'small amount drunk' is the wordplay.
I cannot really understand how this works, but
'small' could be 'mini' (short for miniature) and 'mini' is found in the answer.
'amount' could be 'm' (m is a kind of amount) and 'm' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for minim that I've seen before include "Half-semibreve" , "Quarter of a breve" , "note or > dose" , "Note of two crotchets" , "Note equal to two crochets" .)