Covert offensive interrupted by yokel (7)
I believe the answer is:
thicket
'covert' is the definition.
(thesaurus)
'offensive interrupted by yokel' is the wordplay.
'offensive' becomes 'tet' (Tet Offensive, Vietnam War military campaign).
'interrupted by' is an insertion indicator.
'yokel' becomes 'hick' (synonyms).
'tet' enclosing 'hick' is 'THICKET'.
(Other definitions for thicket that I've seen before include "Dense group of trees or bushes" , "Copse" , "Wood" , "Dense bushy area" , "Dense growth of bushes" .)