Fancy drink with attitude (7)
I believe the answer is:
suppose
'fancy' is the definition.
(both can mean to guess or suspect)
'drink with attitude' is the wordplay.
'drink' becomes 'sup' (to sup is to drink).
'with' means one lot of letters go next to another.
'attitude' becomes 'pose' (attitude can mean a pose or stance).
'sup'+'pose'='SUPPOSE'
(Other definitions for suppose that I've seen before include "'Believe, perhaps on uncertain grounds (7)'" , "Expect" , "Assume without proof" , "Hypothesize" , "Reckon, think" .)