Metric mass unit
I think it could be either:
'metric mass unit' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for gram that I've seen before include "Small metric weight" , "Chickpeas; unit of mass" , "Metric unit of mass" , "pulses" , "Metric unit of weight" .)
'metric mass unit' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for kilo that I've seen before include "Metrical unit of weight" , "possible drugs unit" , "Metric prefix meaning 1,000" , "more than two pounds" , "Measure of weight" .)