Inaugurate girl in old ceremony (9)
I believe the answer is:
originate
'inaugurate' is the definition.
(thesaurus)
'girl in old ceremony' is the wordplay.
'girl' becomes 'gina' ().
'in' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'ceremony' becomes 'rite' (rite is a kind of ceremony).
'o'+'rite'='orite'
'gina' inserted within 'orite' is 'ORIGINATE'.
(Other definitions for originate that I've seen before include "Come into existence" , "Set up" , "In spring" , "Launch" , "Cause to begin, be the first" .)