A bank is the sloping edge to a river or lake, a raised area of ground, or an elevation in the sea bed (eg a sand bank.) A bank can also be a garden feature, allowing trailing plants to be shown to advantage.
It can mean a financial establishment or the act of investing in one (all the money I earn from writing has been safely banked*) The bank is the person who holds the money in gambling games and premises (a bit like the previous definition then.) A banker is a person whose work involves money, and also an insult in rhyming slang.
*not really - I've spent it on books, cake ingredients and plants.
It's the way a race track slopes to help cornering at speed or a row of similar items such a bank of light switches. In the UK a bank holiday is a public holiday. A pilot may find himself banking (travelling with one side higher than the other) to help avoid flying through a fog bank.
Bank is used in several common expressions, usually to suggest reliability or good fortune. Getting a story acceptance will leave you laughing all the way to the bank. Getting rejections is something we can all bank on.