Latin word rex comes from Proto-Indo-European *rek-, and later Proto-Indo-European *h₃rḗǵs (King, ruler.)
| Dictionary entry | Language | Definition |
|---|---|---|
| *rek- | Proto-Indo-European (ine-pro) | |
| *h₃rḗǵs | Proto-Indo-European (ine-pro) | King, ruler. |
| *rēks | Proto-Italic (itc-pro) | King. |
| rex | Latin (lat) | (Late Latin, chess) king. King, ruler. |