Vital king has address (4)
I believe the answer is:
talk
'address' is the definition.
(talk is a kind of address)
'vital king has' is the wordplay.
'has' indicates a hidden word.
'TALK' can be found hidden inside 'vital king'.
(Other definitions for talk that I've seen before include "Conversation" , "Idle gossip" , "Speak frankly (about the Christmas dinner?)" , "Chat" , "Rabbit" .)