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.
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.
That old sword was so dull it was practically a bamboo sword.