"the last scholar of the ancient world" (Montalembert, per Wiki)

https://en.wikipedia.org/wiki/Isidore_of_Seville

his _Etymologiae_ (first encyclopedia of the Christian era)

Complete Latin text here:

https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Isidore/home.html

2006 English translation here:

https://www.cambridge.org/core/books/etymologies-of-isidore-of-seville/F2336BA779D4ED95E6D25AAE2CCBAD25#

and here!:

https://sfponline.org/Uploads/2002/st%20isidore%20in%20english.pdf

_Etymologiae_ is also known as _Origines_, which seems less misleading.

It does contain many etymologies in our modern sense (histories of
words). Most of them are (to our understanding) wrong. Crystal's
example: "Wine (vinum) is so called because it replenishes the veins
(vena) with blood."

About these Isidore writes:

The knowledge of a word's etymology often has an indespensable
usefulness for interpreting the word, for when you have seen whence a
word has originated, you understand its force more quickly.

On the strength of this, Crystal convicts Isidore of committing the
"etymological fallacy"*, but I don't think it's quite that.
A correct etymology can often help us to understand what a word has come
to mean. Even an incorrect etymology may be a useful mnemonic in some
cases.

*"the view that an earlier (or the oldest) meaning of a word is the
correct one" (Crystal, Dictionary of Linguistics and Phonetics, 4th ed.)