One needing to be driven home after ancient-looking cocktail (5,4)
I believe the answer is:
rusty nail
'cocktail' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for rusty nail that I've seen before include "one's likely to get hammered!" , "one drunk at cocktail party?" , "Strong sweet cocktail" .)