Here are what we have in Greek:
"γιορτη" το celebrate a particular event. e.g. Someone's name day, in fact we often just say "ειναι η γιόρτη του" for it is "his name day" rather than "ονομαστικη γιορτη" e.g.
"δεξίωση" as in reception "δεξίωση γάμου"
"πανηγύρι" a mass celebration which may include the whole town/village and border on a fun fair, usually to celebrate the feast day of the local church.
"γλέντι" a lively party
and of course "παρτυ".
Check out the images for ***πανηγύρι" :)
γιορτη is a tricky one alright ! I tried "fiesta" (transplanting an element from the other end of the Med) but it was rejected, reasonably enough. The explanations above are excellent, thanks for that; "celebration" I like. But "feast" is only used if you're roasting swans and malmsey is being poured by serving wenches. I suppose the most British thing would be to say "I'll see you at the do tonight".
Graecophones usually say "γιορτή" for "feast", "celebration" and "πάρτυ" for "party". e.g. You will never hear anyone say "γιορτή γενεθλίων" for "birthday party" but you will hear many say "πάρτυ γενεθλίων" ;) What's more, you can hold a party to celebrate something, a birthday, a wedding anniversary, a promotion, etc. in which case it is both γιορτή (celebration) and πάρτυ, but you can also have one just for the fun of it! In this case you can't say γιορτή, just πάρτυ.
"στη γιορτή" is one of the accepted translations. We are unable to make changes to the original sentences until the new tree is completed.
Did you use "στη γιορτή" and have it rejected. That would mean that you had another error. You didn't make a "My sentence should be accepted." report which would help identify what you typed. When the New Tree now being created is released this will have been edited until then we can only add alternative translations but we cannot edit the original sentence.