Heavy object (6)
I believe the answer is:
weight
'heavy object' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for weight that I've seen before include "Importance, oppressive force" , "The property of heaviness, measure of mass" , "gives a sense of oppression" , "Gravitational pull" , "Avoir-du-pois" .)