As you might know, the earth is not really spherical. Not that it’s flat, of course — but its shape is slightly distorted by the fact that it spins, so it’s an “oblate spheroid” — that is, it’s slightly flattened at the poles. Now, if you read anything about European history in the late Middle Ages, you might find mentions of oblates. But in that context, oblates are religious people, not slightly-flattened spheres (Friar Tuck might be an exception).
An oblate in the religious sense is a person who is attached to a religious group or order, but is not part of the core group — that is, they are not bound by special vows. Oblates, for example, might be part of a monastery, even living and working there, but they’re still officially part of the secular world. This served some purposes very well, evidently, since there would have been some things oblates would be allowed to do that the monks themselves could not (or at least were not supposed to).
“Oblate” comes from the Latin word “oblatus,” meaning “to bring forward”. If you go one step further back in Latin, the root is “offerre,” which is where the English word “offer” comes from. “Offer” originally was used exclusively in relation to religious practices, when an “offer” meant giving something as an act of devotion. The word “oblate” comes straight from that sense, in that an “oblate” is someone who offers devotion and good works to the church. That’s also the source of the word “oblation,” which is a religious offering.
But where, then, did the other meaning of “oblate” come from? The one about the flattened sphere? Well, it comes from Latin as well (sort of), but a different Latin root — in fact, the “oblate” that means a shape is a different word from the “oblate” that has to do with religion. The shape version of “oblate” is derived from “prolate,” from the Latin “prolatus,” which meant to prolong or extend. In the 1600s the people studying math and astronomy used “prolate” as a descriptor of a sphere lengthened on the polar axis. That meant they needed another term to describe the opposite effect; flattening at the poles — so they swapped “pro-” for “ob-,” which in Latin sort of meant “in the direction of,” and came up with “oblate” as a completely new term. Given the nature of European culture and education in the 1600s they were surely aware of the existing term “oblate,” but when science calls for a new word, who’s going to argue?
