What is the Greek word for mister?

There isn't a single direct equivalent of "Mister" in Greek that's used in the same way. The way you address a man depends on the context and your relationship with him.

Here are some options:

* Κύριε (Kýrie): This is the most common and formal way to address a man, similar to "Sir" or "Mr." It's used in formal situations and when you don't know the person's name.

* κύριος (kýrios): This is the word for "mister" or "sir" but it's less commonly used as a direct form of address than κύριε. You would use this word if talking *about* a man, rather than to him.

You would typically use the person's title (e.g., Δόκτορ - Doctor, Καθηγητής - Professor) or first name, depending on the level of formality.