Traffic unit? (4)
I believe the answer is:
kilo
'traffic unit?' 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 "2.2 lbs" , "Metrical unit of weight" , "Approx 2 point 205 lbs" , "Metric weight (abbrev.)" , "possible drugs unit" .)