E, on a gas gauge (5)
I believe the answer is:
empty
'e on a gas gauge' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for empty that I've seen before include "Cleared out" , "Hollow or vacant" , "Unfilled" , "Loneliness parents feel when their children leave home" , "vain" .)