Some from Brazil are negative about army officer (7)
I believe the answer is:
general
'army officer' is the definition.
(I've seen this before)
'some from brazil are negative about' is the wordplay.
'some from' indicates the answer is hidden within the clue.
'about' shows that the letters should be reversed in order.
'lareneg' can be found hidden inside 'brazil are negative'.
'lareneg' backwards is 'GENERAL'.
(Other definitions for general that I've seen before include "Officer of the highest rank" , "top brass" , "Army rank" , "Not particular or specific" , "The senior officer is common and widespread" .)