苦无，或称苦内，是日本忍者经常使用的小型武具。形状如一把短剑或峨嵋刺，多以铁制，体积短小，容易携带及藏匿。之所以经常被忍者选为随身武器的原因是苦无原本是一种工具，在当时的市场上相当于现代的多用途刀或者多用途工具组，即使随身携带被发现也不会有人怀疑。日语是「くない」，根据读音写成汉字「苦内」或「苦无」，以后者较为常用。常规的苦无制式，尺寸大概有10至15厘米长。原本苦无只用于挖掘用途，亦有很多人在攀山时借以凿壁借力，后来成为了经常需要进行攀潜活动的忍者的常用护身武器。

另外有一种更小型的苦无，用法是类近于手里剑的飞行型道具，名叫｢飞苦无｣（とびくない），实质上就是轻巧版的飞镖。由于其形状尖长，不像手里剑般可以旋转力量掷出，所以命中亦比较困难，使用飞苦无的忍者大多拥有高超的掷准技能。

A kunai(苦無,kunai) is a Japanese dagger, possibly derived from the masonry trowel. The two widely-recognized variations of the kunai are short kunai(小苦無,shō-kunai) and the big kunai(大苦無,dai-kunai). Although a basic tool, in the hands of a martial arts expert, the kunai could be used as a multi-functional weapon. The kunai is commonly associated with the ninja, who used it to gouge holes in walls. Kunai were originally made to be farming tools but soon evolved into the weaponry they have become today. Many popular manga and ninjutsu characters use kunai as both their primary and secondary weapons.