Juliet has posh cool drink (5)
I believe the answer is:
juice
'drink' is the definition.
(I've seen this before)
'juliet has posh cool' is the wordplay.
'juliet' becomes 'J' (phonetic alphabet: alpha, bravo, charlie etc.).
'has' means one lot of letters go next to another.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'cool' becomes 'ice' (icing is a kind of cooling).
'j'+'u'+'ice'='JUICE'
(Other definitions for juice that I've seen before include "Fruit extract" , "It can be expressed" , "Vitality" , "Energy" , "power" .)