Origin and history of primatology

"high bishop, preeminent ecclesiastical official of a province," having a certain jurisdiction, as vicar of the pope, over other bishops in his province, c. 1200, from Old French primat and directly from Medieval Latin primatem (nominative primas) "church primate," noun use of Late Latin adjective primas "of the first rank, chief, principal," from primus "first" (see prime (adj.)).

The meaning "animal of the biological order including monkeys and humans" is attested from 1876, from Modern Latin Primates, the order name (Linnæus), from plural of Latin primas; so called for being regarded as the "highest" order of mammals (originally also including bats).

word-forming element indicating "branch of knowledge, science," now the usual form of -logy. Originally used c. 1800 in nonce formations (commonsensology, etc.), it gained legitimacy by influence of the proper formation in geology, mythology, etc., where the -o- is a stem vowel in the previous element.

The second element is prop[erly] -logy ( -logue, etc.), the -o- belonging to the preceding element; but the accent makes the apparent element in E[nglish] to be -ology, which is hence often used as an independent word. [Century Dictionary]