The koy (Mishnaic Hebrew: ) is a kosher animal classified in the Mishnah as an intermediate between cattle and beast.
Ashkenazi Jews traditionally pronounced the word as kvi (Hebrew: ); while Yemenite Jews and most Sephardi Jews pronounced it as koy (Hebrew: ). Nowadays, many Ashkenazi Jews also pronounce it as koy which is the correct spelling according to most scholars.
Different spellings are found in various manuscripts such as the Kaufmann Manuscript and others.
One opinion is that the word is from the same root as cow, and refers to the cow of the Germanic peoples which was halfway domesticated. Another possibility is that the word is from the same root as the Arabic (kawy), meaning strong.
The Talmud cites three opinions regarding the identity of the koy:
Some modern scholars identify the koy as the Bubalus.
The sages were not sure whether the koy has the halakhic status of cattle or beast, and therefore they ruled stringently, sometimes giving it the status of cattle and sometimes giving it the status of beast. The details of these laws are recorded in the Mishnah.