In which properly dressed soldiers are lamenting breaking up (9)
I believe the answer is:
alignment
'in which properly dressed soldiers are' is the definition.
'lamenting breaking up' is the wordplay.
'breaking up' indicates an anagram.
'lamenting' with letters rearranged gives 'ALIGNMENT'.
(Other definitions for alignment that I've seen before include "political position" , "evening out" , "union" , "Act of straightening" , "in a row?" .)