EtymOnline says ( https://www.etymonline.com/word/toxic ) that Ancient Greek τόξον "bow" and Latin taxus "yew" are related, but not because Latin borrowed from Greek -- rather, a Scythian word was probably the ultimate source and that word was borrowed into both Greek and Latin. (EtymOnline doesn't guess at what the meaning or shape of that Scythian word might have been.)
Well, the grammatical rule is that prepositions come directly before a noun, but adverbs or nouns needs a preposition to connect them to a noun.
But that doesn't help if you don't know which words are prepositions and which aren't.
behind is a preposition, so you can say behind the cannons. But front is a noun, so you say in front of the cannons. And next is an adverb, so it's next to the cannons.
Perhaps it's best to learn behind and in front of and next to as units like that, not behind and front and next as individual words.
It's a bit like the difference between εκτός Αθηνών (εκτός is a preposition) but έξω από την Αθήνα (έξω is an adverb so it needs a preposition - από - before a noun). Learners of Greek have to learn which word acts which way.
Modern Greek only has a few "real" preposition, so there are a lot of what you might call "compound prepositions" composed of an adverb and a preposition (μέσα σε, έξω από, ...). English has more prepositions but it also uses combinations of noun or adverb + preposition for come concepts.