Heavy measure (3)
I believe the answer is:
ton
'heavy 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 "A slang 100mph - heavy" , "Unit of weight equivalent to 2240 pounds" , "Imperial unit of weight" , "People of fashion" , "A slang 100 mph" .)