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so these are synonyms?

https://en.wikipedia.org/wiki/Ren%C3%A9_Descartes

>was a French philosopher, scientist, and mathematician, widely considered a seminal figure in the emergence of modern philosophy and science.

...pretty sure he used neither word.

The answer is probably 'nearly'. Like, l'esprit may translate into 'the force which animates' - which could be mind or soul (I'm not a native french speaker - native speakers jump in!). This is sort of the difficultly in translation, l'esprit will have different connotations to a native speaker compared to mind/soul for an English speaker. The meaning is also going to be context sensitive for a given passage. When you're reading just keep in mind the translated words may have a broader connotation or a connotation that isn't native to you. English and French share a lot of roots though, so it's not so bad!

The implication is that OP is reading a translation. Descartes likely used the word 'esprit', different translations may cause confusion around the word.

Yes, that's my point. You'd have to look up what word descartes uses and how it was translated. Depending on context similar words might get different translations and vice versa.

As a native speaker, I would say "esprit" can, depending on the context, mean either "spirit" (of a person, a place, ghost) or "mind". But it seems like it's always one or the other, and never a mix of both. Two distinct meanings.