To s-see a drunkard (7)
I believe the answer is:
'a drunkard' is the definition.
(I've seen this before)
'to s-see' is the wordplay.
's-see' becomes 's-spot' ('spot' said with a stutter like 'see' was; to spot is to notice or catch sight of).
(Other definitions for tosspot that I've seen before include "Fool" , "One drunkard" , "supper, habitually" , "One drinker" , "Habitual drinker" .)