Poet in pub beginning to declaim (4)
I believe the answer is:
bard
'poet' is the definition.
(I've seen this before)
'pub beginning to declaim' is the wordplay.
'pub' becomes 'bar' (I've seen this before).
'beginning to' suggests taking the first letters.
The initial letter of 'declaim' is 'd'.
'bar'+'d'='BARD'
'in' is the link.
(Other definitions for bard that I've seen before include "Shakespeare" , "Celtic poet" , "Eisteddfod winner" , "Animal; cruel person" , "A drab sort of old poet" .)