Tramp knocks back the bar cocktail (4)
I believe the answer is:
walk
'tramp' is the definition.
(thesaurus)
'knocks back the bar cocktail' is the wordplay.
'knocks back' says the letters should be written in reverse (I've seen 'knock back' mean this).
'the bar' becomes 'law' (I can't justify this - if you can you should give a lot more credence to this answer).
'cocktail' becomes 'K' (the end letter or tail of the word 'cocktail').
'law' reversed gives 'wal'.
'wal'+'k'='WALK'
Can you help me to learn more?
(Other definitions for walk that I've seen before include "Be a pedestrian" , "Perambulate" , "Go on foot" , "Amble" , "Stroll" .)