天てん鼠そMeanings1nounbat (animal)archaicArchaic term for bat; replaced by こうもり in modern Japanese. Found in old texts or classical contexts.See also: こうもり古ふるい文ぶん献けんでは、蝙蝠こうもりのことを天てん鼠そと記しるすことがある。In old documents, bats are sometimes written as 天鼠.