noun
For pens, brushes, glasses, and similar items. Often written in kana.
万年筆のさやをなくした。
I lost the cap of my fountain pen.
noun
margin; spread; markup; commission
Financial term: the difference between two prices, such as buying and selling prices. Usually written in kana.
See also: サヤ取り
この取引のサヤは小さい。
The spread on this trade is small.
noun
Rare architectural or historical use for an enclosing structure or outer fence.
古い城の鞘が残っている。
The outer fence of the old castle remains.
The origin is uncertain. The kanji 鞘 is conventionally used for scabbard and sheath, and by extension for other enclosing objects.