Have I been using that term incorrectly? It’s possible. If so, what’s the canonical acronym for “encrypting a function”?

The term you are looking for is "obfuscation". Either black-box obfuscation (which was shown to be impossible) or the indistinguishability obfuscation, which is what the article talks about.

Obfuscation roughly means "encrypting a function." But here be dragons: since the adversary gets non-black-box access to the implementation of the function (a circuit), and can also learn as many (input, output = f(input)) pairs as they want, it becomes impossible to say that the adversary cannot learn anything else about f in the general case (intuitively, consider a higher-order function f: you could learn a lot about f by computing f(f)).