Unlimited standard drink (5)
I believe the answer is:
lassi
'drink' is the definition.
(I've seen this before)
'unlimited standard' is the wordplay.
'unlimited' indicates the central letters (discard the edges or 'limits' of the word).
'standard' becomes 'classic' (similar in meaning).
The centre of 'classic' is 'LASSI'.
(Other definitions for lassi that I've seen before include "Indian dairy drink" , "creamy drink" , "chilled drink" , "drink in India" , "Cold drink" .)