(1) A bank is a thing you fall down.
This is easier to do if you are drunk or stupid (easiest if you are both drunk and stupid, but for that you need the right genetics and have to put in some effort as well). And be able to swallow.
So, say you have a creek.
Say you don't like to get your feet wet so you are standing near the creek but not in it just yet.
Say your name is Jane, and you have been handed a piece of paper with these words on it:
"According to experts the first 4 moves in a chess game can be played in 197299 totally different ways. If it takes 30 seconds to make one move, how long would it take one player to try every possible set of 4 moves?"
Now ask yourself, Jane, do you want to figure this out or would you rather keep reading the rest of this definition? Or poke needles in your eyes?
Well, Jane, if you've gotten this far, let's assume that you decided to keep reading so we'll continue explaining what a bank is. And you can save the needles for later.
Go ahead and take a few steps toward that stream Jane, and if you suddenly drop down a foot or two, or five or ten, then you have found it. The bank. Maybe you've even broken it, but we hope that's all that got broken, because dammit, despite our cranky little peevish and generally undeserving selves, we've almost come to like you.
But back to the real world.
The bank you have just interacted with (or embankment if you want to get fancy) is a place where the earth suddenly isn't anymore.
It's a negative sort of space, an emptiness, a vacancy, and if you walk over the edge of it you get to experience this in a surprisingly sudden way, especially if you are stupid or drunk, or both.
Even if your name is Milo.
Because Jane has gotten tired of this game and has gone home. Without you, Milo. So think about your remaining options while you sober up.
(2) A bank is what you rob to get money for a backpacking trip.
Doing this gives you motivation to keep hiking fast enough to set new records.
It may provide you with room and board (and colorful pals) after your trip is done, even if you bail out before the end of the trail.
But all of this can interfere with future trips, so make sure it's really what you're best suited for. Don't forget that "bail" is a word with different meanings, depending on context, and it is in limited supply, so it can be denied.
And as always, if your name is Milo, give yourself an extra 10 years.
Also known as, of course, embankment. From embank "to enclose with a bank" (1786). Or tribunal. From the Latin: "platform for the seat of magistrates, elevation, embankment". And such like.
Source: How to talk in the woods.