Anicium was a substance which, combined with yurium, could produce a powerful explosion.
During his scheme to commandeer the USS Discovery using temporal loops, Harry Mudd destroyed the ship in one of the loops using an anicium-yurium reaction. (DIS: "Magic to Make the Sanest Man Go Mad")
Bela Tyken used anicium and yurium from his cargo to create a massive explosion and free his ship from a Tyken's Rift. (TNG: "Night Terrors")