Start to hold forth about one spirit (9)
I believe the answer is:
originate
'start' is the definition.
('originate' can be a synonym of 'start')
'hold forth about one spirit' is the wordplay.
'hold forth' becomes 'orate' (I've seen this before).
'about' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'spirit' becomes 'gin' (I've seen this before).
'i'+'gin'='igin'
'orate' placed around 'igin' is 'ORIGINATE'.
'to' is the link.
(Other definitions for originate that I've seen before include "Stem" , "Create, initiate" , "From kick off" , "In spring" , "Invent" .)