Odds on Alice, possibly, must be exceptional (7)
I believe the answer is:
special
'exceptional' is the definition.
('special' can be a synonym of 'exceptional')
'odds on alice possibly' is the wordplay.
'odds' becomes 'sp' (betting abbreviation for starting price**).
'on' indicates putting letters inside.
'possibly' indicates anagramming the letters.
'alice' anagrammed gives 'ecial'.
'sp' put within 'ecial' is 'SPECIAL'.
'must be' is the link.
(Other definitions for special that I've seen before include "Remarkable" , "Quite out of the ordinary" , "Dish not on regular menu" , "Exceptional in intensity or quality" , "Distinctive, exceptional" .)