An antimatter converter was a piece of technology.
In 2369 an antimatter converter was stolen from a Cardassian outpost by the Bajoran Kohn-Ma terrorist Tahna Los. The Cardassian warship Aldara tried to stop him but Tahna received political asylum aboard Deep Space 9.
Tahna later bought bilitrium from the Klingon Duras sisters Lursa and B'Etor. Combined, bilitrium and the antimatter converter, were an incredibly powerful source of energy like a bomb. Tahna planned to destroy the entrance of the wormhole with this bomb and transferred energy from the warp drive of the runabout USS Yangtzee Kiang into the storage cells of the converter but was stopped by Major Kira Nerys, Commander Benjamin Sisko, and Chief Miles O'Brien. (DS9: "Past Prologue")