Write back to Juliet (3)
I believe the answer is:
jot
'write' is the definition.
(jotting is a kind of writing)
'back to juliet' is the wordplay.
'back' is a reversal indicator.
'juliet' becomes 'j' (phonetic alphabet: alpha, bravo, charlie etc.).
'to'+'j'='toj'
'toj' reversed gives 'JOT'.
(Other definitions for jot that I've seen before include "Set down briefly" , "Scrap" , "Write hurriedly" , "Write hastily - a very small amount" , "Small piece - note" .)