Formal:
* Preserve: This is the most direct synonym, implying the act of preventing decomposition.
* Inhume: This refers to the process of burying a body, often after embalming.
Informal:
* Prepare: This is a general term that could refer to the process of preparing a body for burial or cremation.
* Treat: This is a less formal term that can be used in place of embalm.
* Fix: This is a slang term that refers to the process of embalming.
The best word to use will depend on the specific context and the desired tone.