Looking up 无 in a Japanese dictionary was never going to work, but it took a few moments to work that out.
无 (pronounced wú, meaning nothing) is a simplified Chinese character. The traditional form, 無, is in Japanese (and pronounced む mu). A good way to remember it is as a sheaf of wheat sitting on the fire, becoming nothing pretty quickly. It functions much like the Greek privative a-, like a general-purpose un– or non-.
Luckily, the free Unicode text editor app, BabelPad, can convert between Simplified and Traditional.