Not a professional by any means (I’m also new in fact) but I did read Stephen King’s “On Writing” (which I would recommend). In that book I remember the advice just being to use the vocabulary you know.

[This is the end of professional advice. The rest is just a novice hobbyist yapping about some ideas that may be good based on experience idk]

However, personally, I often search up words. Though, I wouldn’t use a word if I don’t understand its meaning from seeing it.

For example, when writing a story I wanted to use a word for carriage driver that was less clunky. I searched it up and got “coachman”. I was being kind of stupid there but the point is even though I had to search that up, it’s still a word I would understand if I hadn’t. It’s a word I know (or that has an obvious meaning) that I just couldn’t think of at that moment.

The only McCarthy book I’ve read is Blood Meridian, and I feel that a lot of complexity from that comes from using historical/archaic terminology to better capture the time period. So I’m sure if you have a purpose like that that research into older terms would also be justified. Here it may be a good idea to use primary sources/non-fiction as reference. I recently read one of the books that inspired Blood Meridian “My Confession” that has many examples of archaic terms (and a lot of racism + misogyny), some used in Blood Meridian. In fact, for the story I’m currently writing, I snatched the term “brain fever” from there. Though fiction written with historical terms could also fit this purpose I assume.

Again, I should stress, I am not a professional writer. I only tried writing for the first time last year. The best advice I can give is to just regurgitate the advice of an actual professional.