Καλημέρα/ Kalimera is a super basic word. It means good morning and is used from early morning till midday.
Καλό μεσημέρι/ Kalo mesimeri means good noon and technically, you’re supposed to use it from 12.00 until 15.00. Kalo mesimeri also conveys the wish to have a good lunch and a nice siesta.
Καλησπέρα/ Kalispera. This word derives from kali "beautiful" or "good", and espera "even" and means good evening. You can also use the phrase Kalo apogeuma instead of Kalispera and you’re supposed to use it from 15.00 or 16.00 until the night.
Καληνύχτα/ Kali nychta means "good night" and is the phrase Greeks use right before bedtime. You can also say Kalo vrady, which has the same meaning.
Γειά σου/ Ya sou (in the singular) is actually an informal way of saying ''hello''. It derives from ygeia ''health'' and sou ''to you''. So when you say Ya sou to someone you are wishing him/her good health. The formal and polite greeting is Ya sas and you have to use ya sas with strangers, older people, etc.
Χαίρετε/ Chairete is the polite way to say hi. Actually it means ''rejoice'' and “greetings”.
Καλώς ήρθες/ Kalos irthes means ''welcome''. If you want, you can also use the phrase Kalos orises, which is the formal way to say welcome in greek.
Τα λέμε/ Ta leme is a very popular expression and it is the informal way of saying ''see you'' . The formal way is Eis to epanidein which literally means ''until we see each other again''.
Ναι/ Nai is ''Yes''
Όχι/ Ochi means ''No''
Eυχαριστώ/ Eycharisto is ''Thank you''
Παρακαλώ/ Parakalo is ''You are welcome''
Δεν ξέρω/ Den ksero is ''I don't know''
Δεν καταλαβαίνω/ Den katalavaino is ''I don't understand''
Γειά μας/ Ya mas is the phrase used for ''Cheers''
Έλα/ Ela is ''Come on'' but you can also use this word when you answer the phone to someone familiar.
Χάρηκα/ Charika is ''Nice to meet you''
Καλή όρεξη/ Kali oreksi means ''Enjoy your meal''
Μιλάς αγγλικά/ Milas anglika is ''Do you speak english?''
Τι κάνεις/ Ti kaneis which means ''How are you?''
Που είναι/ Pou einai is ''Where is...?''
Δεξιά/ Deksia is ''Right''
Αριστερά/ Aristera is ''Left''
Βόλτα/ Volta is ''Walk''
Φιλιά/ Filia is ''Kisses''
Μαλάκας/ Malakas is a slang word which is used to describe jerk but this word has a variety of different meanings depending on the tone and context used. So you can also use this word to a friend instead of "dude", or "mate".
Φιλοξενία/ Filoxenia is ''hospitality'' and derives from the words filo which means ''love'' in ancient greek and ksenos which means ''stranger'', so its the state of being a friend to strangers. For ancient Greeks filoxenia was a core value and Zeus, the King of the gods and ruler of Mount Olympus was also known as Zeus Xenios, “the strangers’ god,” because he was the protector of strangers and travelers.
Φιλότιμο/ Filotimo is maybe the highest of all virtues among Greeks but it is difficult to explain it. It is comprising of the words filo '' to love'' or ''to like'' and timo ''to honor'' and it actually represents a way of life which encompasses an array of virtues like honour, justice, courage, duty, dignity, respect, pride and integrity.
Μεράκι/ Meraki is a really beautiful untranslatable word in Greek which means to do something with passion, with love, with absolute devotion, with all your heart.
Νοσταλγία/ Nostalgia is homesickness and derives from the word nostos which is the ''homecoming'' and the word algos which means ''pain'' or ''ache''.
Κέφι/ Kefi is another word that can not be translated and it is used to describe the spirit of joy, euphoria and happiness.