A kendo practice sword made of four bamboo slats, held together with white leather fittings at the handle, the tip, and around 3/4ths up the length of the "blade".
It is the standard wooden training weapon for sparring and formal competitions in kendo, as its construction gives it more flex which makes it unlikely to injure competitors when the associated armor is being worn (see bougu).
Do not confuse with a bokken, which is a practice sword made out of solid wood. A bokken more closely resembles a real katana in shape and does not have leather fittings. A shinai is straight rather than curved, and has visible separation between its constituting pieces of bamboo.
Examples
Shinai without the guard and leather fitting around the handle
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