1000 grams (4)
I believe the answer is:
kilo
'1000 grams' 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 "Measure of weight" , "Metrical unit of weight" , "Lewis Carroll heroine" , "Metric weight, informally" , "Metric prefix meaning 1,000" .)