Fusion weapon
'fusion weapon' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for h-bomb that I've seen before include "Explosive weapon" , "Thermonuclear weapon" , "Hydrogen weapon" , "powerful arm" , "Nuclear weapon" .)
'fusion weapon' is the definition.
(I've seen this before)
This is all the clue.