I'm always fascinated by word origins. Tonight I idly wondered where the names of common kinds of tree came from. The first that popped into my head was 'beech'.
So I headed off to the Oxford English Dictionary, and began a long journey. The word in Old English was bóeke, similar to the tree's name in many Germanic languages. But going back further it is related to Latin fagus, 'beech', and to Ancient Greek φαγος or φηγος (modern Greek φηγος).
But here is an interesting bit. The root of the Greek word is from eating*. It seems to have originally meant 'a tree with eatable fruit'. You can eat beech nuts, 'mast', and they are quite tasty, though small and therefore fiddly. I've heard they might be hallucigenic, although I think you would have to pig a lot to notice anything.
Now we come to 'book'. This is a highly contested but still strongly supported and very plausible origin. Germanic peoples wrote on strips of wood (rather than papyrus or wax tablets). Collections of such wood-strip writings were called bóeken (I think that would be the OE plural, I haven't checked.) And Modern German for beech is Buche.
So if all this is right, the word 'book' ultimately goes back to ancient words connected with food and eating. So we could say, that in a sense, books are food for thought.
* One of the first Greek expressions I learned was να φαμε, let's eat, which I think is the same verb stem.