bamboo sword; bamboo imitation sword
A toy or prop sword made of bamboo, shaped like a katana or similar blade. Often used in children's play or as a stage prop.
子供たちは竹光を振り回して遊んでいた。
The children were playing, swinging bamboo swords around.
dull sword; blunt sword
Figurative extension: a sword so dull it might as well be bamboo. Can be used humorously or disparagingly.
その古い刀はまるで竹光のように切れなかった。
That old sword was so dull it was practically a bamboo sword.
Compound of 竹 (bamboo) and 光 (light, shine), likely referring to the shiny surface of a bamboo sword polished to resemble a real blade. The exact origin is uncertain.