Body of troops used to build a bridge (7)
I believe the answer is:
brigade
'body of troops' is the definition.
(I've seen this before)
'to build a bridge' is the wordplay.
'to build' indicates anagramming the letters.
'a'+'bridge'='abridge'
'abridge' is an anagram of 'BRIGADE'.
'used' acts as a link.
(Other definitions for brigade that I've seen before include "Army subdivision" , "Corps" , "Army grouping" , "Part of an army division" , "Soldiers" .)