Finally legless, fuss over drink (4)
I believe the answer is:
soda
'drink' is the definition.
(soda is a kind of drink)
'finally legless fuss over' is the wordplay.
'finally' suggests the final letters.
'fuss' becomes 'ado' (synonyms).
'over' shows that the letters should be reversed in order.
The last letter of 'legless' is 's'.
'ado' back-to-front is 'oda'.
's'+'oda'='SODA'
(Other definitions for soda that I've seen before include "Type of bread, water or fountain" , "Variety of pop" , "Fizzy water, goes well with whiskey" , ""Splashed" drinks mixer" , "for use with whisky?" .)