In the late 19th century, dude was an epithet for fastidiously dressed East-coast “city boys” who came out west to vacation on cattle ranches. The only current use that hearkens back to the original meaning is the verb, to dude up, which means to get dressed up in stylish clothes. But dude is now most widely used as a synonym for “man” or “guy.”

Perhaps the most American use of the word “dude” might be as an interjection for emphasis. When used this way, it no longer only means “some guy” and can start to mean anything:

• girlfriend: “Who’s that dude over there?”
• boyfriend: “Dude, I can’t see where you’re pointing!”
• girlfriend: “Look, the one by the bar who’s all duded up like he’s a movie star or something. Doesn’t he look familiar?”
• boyfriend: “Dude, that’s Keanu Reeves!”
• girlfriend: “Dude, you’re right!”
• boyfriend: “Duuuuuuuude.“

Dude conveys such a wide range of meanings, especially as an interjection, that entire conversations can be conducted with only that word. The bonus definition for dude is, of course, Jeff Bridges’ character from The Big Lebowski: The Dude. If you still can’t understand how to use this word, watch that movie, like now, dude!