It is derived from a Chinese word and there is a sentence, 'The death of emperors is called 崩 (ho), the death of lords is called 薨 (ko), the death of daibu (master) is called 卒 (sotsu), the death of warrior is called 不禄 (furoku), and the death of ordinary people is called 死 (shi)' in the Kyokurei volume of "Book of Rites".
元々は中国起源の語であり、『礼記』曲礼篇に「天子の死は崩と曰ひ、諸侯は薨と曰ひ、大夫は卒と曰ひ、士は不禄と曰ひ、庶人は死と曰ふ」とある。