One serving American in fancy launch (9)
I believe the answer is:
originate
'launch' is the definition.
(thesaurus)
'one serving american in fancy' is the wordplay.
'one' becomes 'i' (Roman numeral).
'serving american' becomes 'gi' (I've seen this in other clues).
'in' is an insertion indicator.
'fancy' becomes 'ornate' (I've seen this before**).
'i'+'gi'='igi'
'igi' put into 'ornate' is 'ORIGINATE'.
(Other definitions for originate that I've seen before include "Come into existence" , "Invent" , "Found" , "In spring" , "Set up" .)