[mmooss]

To add a bit of detail: At least in English etymologies, there are significant differences between classical Latin and post-classical Latin.

But post-classical Latin unhelpfully covers Rome from ~200 CE into the 20th century, including the Catholic Church and all those scholars and scientists. I'm not sure what differences arose before or after the fall of Rome in 476 CE, which began the Middle Ages.

[dhosek]

There were shifts in the meaning of words as well as shifts in some grammatical structures. English has seen similar shifts in meaning, e.g., villain originally meant a person from a village.