One of my favourites is the word jam, which can mean:

• A fruit preserve
• Traffic that's stopped
• To play music
• A door that won't open
• A difficult situation
• To force something in somewhere it's not supposed to be
• To interrupt a signal
• Something you don't like or can't do ("that's not my jam")

And probably others, all spelled and pronounced the same way but with wildly different meanings depending on the context.

The other English thing I find super interesting is how there's a sort of unspoken but very clearly understood order to adjectives. So for example, if I say "The big old red wooden door" it works as a description, but if I say "The wooden old red big door" it sounds weird even though it's the same information. People aren't usually formally taught the order (as far as I know), but everyone seems to understand it.