Where does “Siem Reap” come from?

Siem Reap (English) comes from Khmer សៀមរាប, from Khmer រាប, from Thai รับ, from Proto-Southwestern Tai rapᴰ²ˢ — to accept; to receive.

Ancestry of “Siem Reap”, step by step

Step	Language	Word	Meaning
1	Khmer	សៀមរាប	—
2	Khmer	រាប	smooth, level, even, flat; quiet, motionless;...
3	Thai	รับ	to greet; to receive; to welcome; to acquire; to...
4	Proto-Southwestern Tai	rapᴰ²ˢ	to accept; to receive