I've been learning European Portuguese for a few months and in the class, we always used amigo for a friend. But recently I've encountered the word amigão, which was also translated as a friend.
Here in the online dictionary I've found that amigão = grande amigo, but a friend of mine (who is a beginner like me) claims that: amigão = very good friend.
So my question is: what does amigão really mean? Is it used to describe a friend who is literally big, or maybe a good friend, or a best friend, or maybe sth else? And what is the difference between amigo and amigão?