Weight of explosive power (7)
I believe the answer is:
megaton
'weight' is the definition.
(megaton is a kind of weight)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for megaton that I've seen before include "Unit of explosive power" , "Measure of explosive power - montage (anag)" , "Explosive power equivalent to one million tons of TNT" , "weight" , "it weighs a lot" .)