Declare publicly (8)
(Other definitions for proclaim that I've seen before include "Speak out" , "advertise" , "Herald" , "Announce officially or declare publicly" , "Declare formally" .)
'declare publicly' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for avow that I've seen before include "Assert or confess openly" , "Admit openly" , "Asseverate" , "State openly" , "Assert, swear" .)