"Ναι, γεια σας!"

[KeithJones949537]

There seem to be an awful lot of words that all appear to mean both hello and goodbye. Is it ok to use any one of them at any occasion or is there some subtle difference of meaning between them?

[troll1995]

Γεια σου is hello for one person and informal, γεια σας is hello for greeting many people or for being formal to one person. Γεια σας/σου is also used as goodbye, αντίο is more like farewell.

[KeithJones949537]

Think I have it. Thank you.

[Dmatafonov]

what is the difference between γεια σας και γεια σου;

[mizinamo]

Γεια σας! is used when speaking to several people, or when speaking politely/formally.

Γεια σου! is used when speaking to one person whom you know well.

It's a T/V distinction (like tu/vous in French or ты/вы in Russian or du/Sie in German or tú/Usted in Spanish) as well as a singular/plural distinction in the T form.

(So as in French or Russian, the same form is used for speaking to one person formally, or to several people.)