Translation guide
A scabbard is a sheath for a sword, dagger, or bayonet. In Japanese, the most common word is 鞘 (さや), which covers most contexts. There are also specific terms for certain weapons or styles.
The learner wants to refer to the protective case for a blade, typically a Japanese sword (katana) or similar.
The standard word for scabbard or sheath, used for Japanese swords, knives, and other bladed tools. Can be used in most contexts.
Sheathe the sword.
その鞘は美しい漆塗りだ。
That scabbard has a beautiful lacquer finish.
Literally 'sword's scabbard'. Used when you need to be explicit about it being a sword scabbard.
刀の鞘が破損している。
The sword's scabbard is damaged.
The learner is talking about the scabbard of a katana, often in historical or martial arts contexts.
Refers to the scabbard as part of the sword's mounting (koshirae). Used in discussions of sword fittings.
この拵えの鞘には金具が使われている。
This mounting's scabbard uses metal fittings.
A plain wooden scabbard used for storing a blade when not in a formal mounting. Common in sword maintenance.
刀を白鞘に入れて保管する。
Store the blade in a plain wooden scabbard.
The learner is referring to the sheath of a bayonet or combat knife.
Specifically 'bayonet scabbard'. Use when clarity is needed.
銃剣の鞘をベルトに付ける。
Attach the bayonet scabbard to the belt.
Still acceptable if context makes it clear you mean a bayonet or knife sheath.
その鞘は頑丈な革製だ。
That scabbard is made of sturdy leather.
While 鞘 (さや) is the traditional word for scabbard, the loanword シース (shiisu) from English 'sheath' is sometimes used for modern tactical or outdoor knife sheaths. However, 鞘 remains more common and natural in most contexts.