Some of the words in music theory are just straight latin, or directly descendant from latin and old. A lot of people struggle with music theory until you "translate" it to using modern language (though you do lose some specificity in some cases). Like "ritardando", which is just "slow down", or accelerando, which is, you guessed it, "speed up".
Italian, not Latin. Italian is the language of music. Italy used to be the capital of European music. That's where it comes from. I also wouldn't classify it as mere "theory". It's basic notation that appears in notes. Calling it "theory" is like calling control flow constructs in Pascal (the language) "theory".
You can also use arcane.