Long or short measure (3)
I believe the answer is:
ton
'long or short measure' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ton that I've seen before include "1000 kilos" , "A slang 100mph - heavy" , "Speed" , "Two thousand, two hundred and forty lbs avoirdupois" , "20cwt" .)