Rest of soldiers given uniform in camp (7)
I believe the answer is:
residue
'rest' is the definition.
(synonyms)
'soldiers given uniform in camp' is the wordplay.
'soldiers' becomes 're' (Royal Engineers).
'given' is a charade indicator (letters next to each other).
'uniform' becomes 'u' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' means one lot of letters goes inside another.
'camp' becomes 'side' (both can mean a group or faction).
'u' placed into 'side' is 'sidue'.
're'+'sidue'='RESIDUE'
'of' acts as a link.
(Other definitions for residue that I've seen before include "rest" , "waste" , "What is left over, remainder (7)" , "Lees, dregs" , "Stuff left over" .)