Where does “Kambuja” come from?

Kambuja (Middle Khmer) comes from Sanskrit काम्बोज, from Hindi कम्बोज — Kamboj.

Ancestry of “Kambuja”, step by step

Step	Language	Word	Meaning
1	Sanskrit	काम्बोज	born in or coming from Kamboja; a native of...
2	Hindi	कम्बोज	Kamboj