What is "double edge"

Usage examples of "double edge".

He finally bends down and searches the figures, but none bears anything that might prove useful, except for the gold and silver coins in their wallets, two daggers, a truncheon, and a short straight sword with a double edge.

But like the other changes in his personality, Roger's new awareness of the realities of the political instability which plagued the Empire of Man, and of the fact that the MacClintock Dynasty truly was the only glue holding that empire together, had proved to have a nasty double edge from the perspective of the commander of his personal security detachment.