What nuts were known in Biblical times, and to chazal?
Luz=shkeydia = almond
egoz = walnut
botnim = pistachio

which others are in Tanach and divrei chazal?

Also, the minhag of not eating nuts because egoz is almost the same as chet, why doesn't that apply strictly to walnuts?

So how did it change into meaning "peanuts" in MH?

I don't know. But botnim are mentioned in mesechet shevi'it and are definately a tree product so are not peanuts. Secondly, peanuts are a new world food [not that I doubt for a moment that Chazal didn't know of every New World food but for their own esoteric reason refrained from revealing that knowledge in extant writings ]

Obviously the word would not describe a New World food, and Rashi also says botnim are pistachios in Breshis 43...

The question is on MH. Basically if there was a native Hebrew word for them, why borrow an Arabic word (fistuk) and then use the Hebrew word for something else, instead of keeping "botnim" for pistachios and using a loanword or neologism for peanuts.
The Hebraists sure worked in mysterious ways...

Yeah, I don't know. Usually the hebrew words for modern words are pretty clever [eg, in another thread there was a discussion of chashmal for electricity] and are readily adopted by all camps within the spectrum of orthodoxy [again, the discussion on chashmal as a case in point]. I have no idea why botnim are the word for peanuts.

Theres quite a few MH words that make you go . Not all the words were as 'cleverly' created as chashmal.

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