It is always great to know a few words when you go somewhere. When you are in Greece, it can really improve your stay. Although English is popular, it is very different if you say a few words in Greek - it can lead to warmer reception and much more pleasant and fruitful communication.
Ναι [ne] - Yes
Όχι [`ɔhɪ] - No
Γεια σου [`jʌ`sʊ] - Hi/Bye (informal)
Γεια σας [`jʌ`sʌs] - Hello/Good bye (formal)
Καλημέρα [kʌlɪ`merʌ] - Good morning (before noon)
Καλησπέρα [kʌlɪs`perʌ] - Good afternoon/evening (after noon and in the evening)
Καληνύχτα [kʌlɪ`nɪhtʌ] - Good night
Ορίστε [ɔ`rɪste] - Here you are
Ευχαριστώ [evhʌrɪs`tɔ] - Thank you
Συγνώμη [sɪg`nɔmi] - Excuse me (it can also be used to attract someones attention)
Articolo di Petar K