Sergeant perhaps taking part in foreign coup (3)
I believe the answer is:
nco
'sergeant perhaps' is the definition.
(I know that sergeant is a type of NCO)
'part in foreign coup' is the wordplay.
'part in' indicates a hidden word.
'NCO' can be found hidden inside 'foreign coup'.
'taking' acts as a link.
(Other definitions for nco that I've seen before include "eg Corporal" , "In brief, a corporal or sergeant" , "eg RSM" , "Initially, a corporal or sergeant" , "lancejack, say" .)