American — bet (6)
I believe the answer is:
I believe this clue is a double definition.
'american' is the first definition.
(I know that Yankee is a type of american)
'bet' is the second definition.
(type of bet in gambling)
(Other definitions for yankee that I've seen before include "N. American" , "Union soldier in the American Civil War" , "A northerner during the American Civil War" , "American - bet" , "Y in communications" .)