In Greek: καλή όρεξη, pronounced kah-LEE OR-ex-ee
Literally translated, "kali orexi" means "good appetite," or, as the French say, Bon Appétit! Kali Orexi is a wish for all diners: Enjoy your meal!
An example of how you would use it in a sentence is, "I wish you kali orexi. Now, let's eat."