Uncommunicative soldier (7)
I believe the answer is:
private
This clue is a double definition.
'uncommunicative' is the first definition.
(thesaurus)
'soldier' is the second definition.
(I've seen this before)
(Other definitions for private that I've seen before include "Lowly soldier" , "Personal or secret" , "Not open to scrutiny" , "(Of a place) secluded" , "Confidential sort of soldier" .)