noun
A sword used by ninja, often shorter and straighter than a katana, designed for stealth and close-quarters combat.
忍び刀は、忍者が使う特殊な刀です。
A ninja sword is a special sword used by ninja.
Compound of 忍び (shinobi, 'stealth; ninja') and 刀 (katana, 'sword'). The exact historical origin is uncertain, but the term refers to swords associated with ninja.