Whole section in joint action (6)
I believe the answer is:
intact
'whole' is the definition.
('intact' can be similar in meaning to 'whole')
'section in joint action' is the wordplay.
'section' says the answer is hidden in the clue.
'INTACT' can be found hidden inside 'in joint action'.
(Other definitions for intact that I've seen before include "Not damaged or missing a part" , "Inviolate" , "Not broken or damaged" , "Undamaged, unimpaired" , "Entire, undamaged" .)