ترجمة - صيني-انجليزي - nao-tzu

I apologize for the one-word request. It's in a fiction book I'm translating from English. I am asking for a Chinese speaker to translate it for me, as I want to confirm my guesses from context -that the meaning is something like "spirit" or "ghost"... Thanks!

Chinese: 脑子
Modern pinyin: naozi