rhesus monkey vs rhesus

rhesus monkey and rhesus both are nouns.

Word	Noun	Adjective	Verb	Adverb
rhesus monkey	Yes	No	No	No
rhesus	Yes	No	No	No

As nouns, rhesus monkey and rhesus are synonyms defined as:

Other synonyms of rhesus monkey include Macaca mulatta.

rhesus monkey (noun)	rhesus (noun)
of southern Asia; used in medical research	of southern Asia; used in medical research