Monofilament is the common contraction for "monomolecular filament", a long, strong chain of molecules that effectively create the sharpest possible physical cutting edge, allowing them to cut through virtually anything. No form of defense was known to repel monofilament strands. The Federation is aware of the technology; however, they have been incapable of utilizing it as the strands become unstable and collapse. The Tholians used monofilament blades as ceremonial dueling weapons. Captain Hikaru Sulu was forced to duel with one aboard the USS Excelsior in 2298. (TLE novel: The Sundered)