rhesus

[ree-suh s] /ˈri səs/
noun
1.
a macaque, Macaca mulatta, of India, used in experimental medicine.
Origin
1830-40; < Neo-Latin, arbitrary use of Latin Rhēsus name of a Thracian king allied with Troy < Greek Rhêsos
Related forms
rhesian
[ree-shuh n] /ˈri ʃən/ (Show IPA), adjective
British Dictionary definitions for rhesus

Rhesus

/ˈriːsəs/
noun
1.
(Greek myth) a king of Thrace, who arrived in the tenth year of the Trojan War to aid Troy. Odysseus and Diomedes stole his horses because an oracle had said that if these horses drank from the River Xanthus, Troy would not fall
Word Origin and History for rhesus

1827, from Modern Latin genus name of a type of East Indian monkey (1799), given by French naturalist Jean-Baptiste Audebert (1759-1800), said to be an arbitrary use of Latin Rhesus, name of a legendary prince of Thrace, from Greek Rhesos.