It was originally called 'kumo' or 'kyomo' (both meaning 'existing as if nothing exists') but was eventually interpreted as emptiness of everything and came to be called '物滅' (death of everything) (butsumetsu) and recently the letter '佛(仏)' (Buddha) (butsu) was applied instead of 物 (things) (butsu).
元は「空亡」「虚亡」と言っていたが、これを全てが虚しいと解釈して「物滅」と呼ぶようになり、これに近年になって「佛（仏）」の字が当てられたものである。