Volume measure (5)
'volume measure' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for liter that I've seen before include "American volume" , "unit across the pond" .)
(Other definitions for litre that I've seen before include "French volume" , "One thousand cc" , "Metric liquid measure" , "less than two pints" , "1.7598 UK pints" .)