When I say “I went to the bank,” I could mean that I was exchanging US dollars for Turkish lira. I could also mean that I went to catch frogs. Whether I mean money-bank or river-bank depends on context. 

I’ve been asked a few times why words can mean more than one thing. It doesn’t make immediate sense, after all, why natural language would have homophones — doesn’t it make more sense to have a one-to-one ratio between meaning and words?

Actually, languages tend toward the least number of words possible. Fewer words make a language easier to acquire.

Of course, too few words would make a language too ambiguous. So, if a word has multiple senses, the correct sense must be easy to resolve from context.  

A language will — at least theoretically — minimize both lexical size and ambiguity. In the constant evolution of natural languages, the number of homophones in any language is a continuously-shifting compromise between the number of words in a language and the need for a word to be immediately understood.

A look at natural human languages reveals that homophones are generally not easily confusable except in rare contexts. If a word becomes too easily confused — again, theoretically — speakers will replace it with another.

If you want a real-life example, think about what happens when a person (let’s say, someone named John) joins a tight-knit group of friends who already have a friend named John. After a while, the group assigns one (or both) Johns a nickname to easily distinguish the two individuals.