The difference between the words “between” and “among.”
I used the word “between” because I was talking about a choice that involves two distinct words. Between should be used where the relationship is distinctly one-to-one:
“Let's keep this between you and me.”
Among should be used where the entities are considered as a group, mass or collectivity:
“He was glad to find a friend among enemies.”
“She felt like a stranger among friends.”
In fact it's not that simple. You can use the word “between” when you are talking about distinct, individual items even if there are more than two of them. For example, you could say, "She chose between Harvard, Brown, and Yale" because the colleges are individual items”, “The differences between English, Finnish, and Russian are significant.”
“Between” and “among” can also tell the reader different things about location or direction. Think about the difference between these two sentences:
Peter walked between the trees.
Peter walked among the trees.
“Peter walked between the trees” gives you the idea that he stayed on the path; he either walked between two trees or was on a route that was surrounded by trees.
On the other hand, “Peter walked among the trees” gives you the idea that he wandered around a park or forest. He may have had an endpoint in mind, but it doesn't sound as if he went from point A to point B on a defined path.
“Among” Versus “Amongst”
What is the difference between “among” and “amongst”? Both words mean the same thing, but “amongst” is the older form and is more commonly used in Britain than in the United States. It's considered archaic and overly formal or even pretentious in American English. The only time I can think of when it would be appropriate for an American writer to use it would be in fiction set in a different era or world. Something like: “Is it truly safe to walk amongst the peasants, my lord?”