Joint endeavour's revealing plan (6)
I believe the answer is:
intend
'plan' is the definition.
(intending is a kind of planning)
'joint endeavour's revealing' is the wordplay.
'revealing' indicates the answer is hidden within the clue.
'INTEND' can be found hidden inside 'joint endeavours'.
(Other definitions for intend that I've seen before include "Signify" , "Contemplate - mean - plan" , "1 dn [DESIGN]" , "Aim, plan" , "Mean; propose" .)