rhesus

rhesus · noun¹

1. Ancient Greek · derived fromῬῆσος
2. Latin · derived fromRhēsus
3. New Latin · derived fromrhēsus
4. English todayrhesus

From New Latin rhēsus, arbitrary formation from Latin Rhēsus, from Ancient Greek Ῥῆσος (Rhêsos), mythical Thracian king.

Rhesus · noun²

So named because the first identified antigen (RhD) was originally believed to be the same as one discovered in rhesus macaques.