Source of milk shake Juliet put away (5)
I believe the answer is:
udder
'source of milk' is the definition.
(eg a cow's udder)
'shake juliet put away' is the wordplay.
'shake' becomes 'judder' (synonyms).
'juliet' becomes 'J' (phonetic alphabet: alpha, bravo, charlie etc.).
'put away' suggests deleting specific letters.
'judder' with 'j' removed is 'UDDER'.
(Other definitions for udder that I've seen before include "Milk supply" , "Cow's milk "bag"" , "What's at rear on cows" , "Steer with this" , "Part of beastly female" .)