Sat by drink and thought (8)
I believe the answer is:
supposed
'thought' is the definition.
('suppose' can be a synonym of 'think')
'sat by drink' is the wordplay.
'sat' becomes 'posed' ('pose' can be a synonym of 'sit').
'by' means one lot of letters go next to another.
'drink' becomes 'sup' (I've seen this before).
'posed' after 'sup' is 'SUPPOSED'.
'and' acts as a link.
(Other definitions for supposed that I've seen before include "So-called" , "Reckoned, took to be the case" , "Imagined; assumed" , "Assumed to be true or thought probable" , "Generally believed" .)