Grenoble glassful (3)
I believe the answer is:
eau
'grenoble glassful' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for eau that I've seen before include "-- de vie" , "French water, may be Cologne" , "Popular toilet water - . . . de Cologne" , "French water from chateaux" , "Quick to notice things" .)