Explosive device (by which to be hoist?) (6)
I believe the answer is:
petard
(Other definitions for petard that I've seen before include "A small bomb - don't be hoist by your own" , "Case of explosive" , "Explosive device (with which one may be hoist)" , "Explosive device, one could have been hoist by their own, of old" , "Small bomb; one to be hoist with" .)