Bill at a bar (3)
I believe the answer is:
tab
'bill at a bar' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tab that I've seen before include "Flap; meal bill" , "Flap; illicit drug pill (slang)" , "Running bar bill" , "Till bill" , "Kind of label for bat" .)