Argument included clue about European gamble (9)
I believe the answer is:
speculate
'gamble' is the definition.
(thesaurus)
'argument included clue about european' is the wordplay.
'argument' becomes 'spat' (a spat is a disagreement or argument).
'included' indicates putting letters inside.
'about' is an anagram indicator.
'european' becomes 'E' (abbreviation e.g. EU).
'clue' with letters rearranged gives 'ecul'.
'spat' going around 'ecul' is 'speculat'.
'speculat'+'e'='SPECULATE'
(Other definitions for speculate that I've seen before include "Buy in hope of profit, but with risk of loss" , "Form opinion without definite knowledge" , "As before, observe" , "Gamble - guess" , "Imagine" .)