Set up soldier with Juliet to join square dances (4)
I believe the answer is:
jigs
'dances' is the definition.
(jigging is a kind of dancing)
'set up soldier with juliet to join square' is the wordplay.
'set up' says the letters should be written in reverse.
'soldier' becomes 'gi' (government issue or general issue).
'with' is a charade indicator (letters next to each other).
'juliet' becomes 'j' (phonetic alphabet: alpha, bravo, charlie etc.).
'to join square' becomes 's' (I am not sure about this - if you are sure you should believe this answer much more).
'gi' reversed gives 'ig'.
'ig' put after 'j' is 'jig'.
'jig'+'s'='JIGS'
(Other definitions for jigs that I've seen before include "Participant in ballot" , "Irish dances" .)