Start to pontificate, having drunk one drink! (9)
I believe the answer is:
originate
'start' is the definition.
(I know that start can be written as originate)
'pontificate having drunk one drink' is the wordplay.
'pontificate' becomes 'orate' (I've seen this in another clue).
'having drunk' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'drink' becomes 'gin' (gin is a kind of drink).
'i'+'gin'='igin'
'orate' going around 'igin' is 'ORIGINATE'.
'to' acts as a link.
(Other definitions for originate that I've seen before include "issue" , "Create, initiate" , "Cause to begin, be the first" , "Create; begin" , "Invent" .)