The modern Japanese word for mummy is "miira" (katakana - ミイラ) derived from Portuguese "mirra", meaning "myrrh", which is turn comes from Latin "myrrha" and may derive from Akkadian "murru" via Greek.
The Chinese word (from the new Oxford Chinese Dictionary) is 木乃伊, pronounced something like "munaiyi" (can't do the diacritics).
Some questions:
1) Does anyone know of a citation for "mirra" in Portuguese sources on Japan, and when this came into use as "miira" in Japanese?
2) Does anyone know the etymology of the Chinese term?
3) The Japanese Buddhist priests who self-mummified were sometimes known as undergoing a process of attaining Buddhahood in this body (sokushin joubutsu 即身成仏), but was there a specific term for them which signified "mummy"?
4) The term "hotoke" can mean both "Buddha" and "corpse", but when did this identification arise?
(Attached are the kanji in case they are garbled in this message.)
These questions are prompted by the arrival of the Tarim mummies in the exhibition "Secrets of the Silk Road" at the University of Pennsylvania Museum.
http://www.penn.museum/--
Ross Bender
http://rossbender.org