貞宗 Sadamune

What is Sadamune in Japanese Katana terminology?

Sadamune, also known as "Hikoshiro Sadamune", was a swordsmith who was active from the late Kamakura period to the early Nanboku-cho period. He was a direct disciple and also an adopted son of Masamune. There are no existing works of Sadamune with his signature, hence all are unsigned. Furthermore, his three excellent disciples are referred to as the "Sadamune San Tetsu".