Declare openly (4)
I believe the answer is:
avow
'declare openly' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for avow that I've seen before include "Assert, swear" , "Solemnly promise" , "acknowledge" , "Assert or confess openly" , "Declare a promise of fidelity at the altar" .)