Unit of weight, for short (4)
I believe the answer is:
kilo
'unit of weight for short' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for kilo that I've seen before include "Metric weight, informally" , "Unit of weight (abbr)" , "Unit of mass" , "2.2 lbs" , "Lewis Carroll heroine" .)