noun
bamboo sword; shinai
Specifically the bamboo practice sword used in kendo. The reading しない is standard; ちくとう is a rare alternative reading.
剣道の練習では竹刀を使います。
We use bamboo swords in kendo practice.
新しい竹刀を買った。
I bought a new shinai.
noun
Only with reading ちくとう
Rare reading ちくとう for the same object; almost always read しない in modern Japanese. This reading is restricted to the kanji form 竹刀.
「竹刀」を「ちくとう」と読むことはほとんどありません。
The reading ちくとう for 竹刀 is almost never used.
The kanji 竹 (bamboo) and 刀 (sword) directly describe the object. The reading しない is a special kanji reading (gikun/jukujikun) whose origin is uncertain; it may be related to the verb 撓う (しなう, 'to bend'), referring to the bamboo's flexibility.