Where does “ម្រឹត្យុ” come from?

ម្រឹត្យុ (Khmer) comes from Sanskrit मृत्यु, from Sanskrit मृ, from Proto-Indo-Iranian *mar-.

Ancestry of “ម្រឹត្យុ”, step by step

StepLanguageWordMeaning
1Sanskritमृत्युdeath, dying; Death personified, the god of...
2Sanskritमृto die
3Proto-Indo-Iranian*mar-—
Every word from Proto-Indo-Iranian *mar- →Every word from Sanskrit मृ →Every word from Sanskrit मृत्यु →