The koan in question is Chinese, not Japanese; Japanese allows for the reading of old Chinese with Japanese readings, but Japanese people won't understand it wi

The koan in question is Chinese, not Japanese; Japanese allows for the reading of old Chinese with Japanese readings, but Japanese people won't understand it without specific knowledge of how to read Japanized Chinese, so it's in a really weird place in general -- it's definitely not something I'd call a "Japanese word," though.