This is making me crazy.
When you want to talk about the correct, classical quality of some random Latin text, you talk about the latinity. Then you can say things like “Cicero would never have used a subjunctive that way” and you go correct the phrasing.
I haven’t been able to find an appropriate word for this in Greek which we can also use in English. My first guess was something like Helleneia, but that does not appear in the L&S.
Any ideas?
We do have a word “Hellenism”, but I don’t think you are going to find an exact equivalent of “Latinity”…
ἐλεύθερος : ἐλευθερία :: 7(ελληνικός : 7(ελληνικεία???
Greekiness?
Atticity?
Ortholexis?
Orthohellenicisim?
Hellenipraxis?
Quick, alcohol somebody…
Hellenicity sounds best to my ear, but I don’t think that word has sufficient Hellenicity to suit William. 
In French, we have “grécité” a derivative of “grec”, thus a pure French word without Latin background. The English dictionary don’t seem to know any “grecity”. In Latin, we find atticismos, i “use of the Attic style”. Maybe you have to use a periphrase in English.
But the word “Greek” is derived from Latin! And Greek already has “Hellenisme”. I like “Hellenikeia”, but it’s apparently not attested by any extant Greek text.
Well, the problem with “greekiness” is that it is too much like what I do most of the time, namely geekiness.
Atticity/atticism/ktl. all necessarily imply a particular dialect of Greek. We leave out Herodotus, which is a shame.
Grécité is nice, but I agree with Skylax that we may have to make do with a periphrase in English.
Shall we use it anyway? Greek didn’t really die when Alexander took Athens.
I’m all for it, but of course I would be, since I coined the word. Or does one “Koine” new Greek words?
Not sure about koinizing (?) it, but we should verify that -ikeia occurs in some other Gk word. Hellenia or Helleneia may be sufficient. But I don’t know for certain without some quality time with the word formation sections of Smyth.
It’s interesting, in German it’s almost the same as in French. We use “Latinität” and “Gräzität”…
Ahh… didn’t know that. I just don’t use these words.
I thought ikeia was Swedish .
Maybe “grecism” ? The dictionary says “1. The style or spirit of Greek culture, art, or thought. 2. Something done in imitation of Greek style or spirit. 3. An idiom of the Greek language.”
That sounds good to me.
Many feminine german nouns in -ät come from French i.e Qualité = Qualität. At least I know something about german 
Actually, the Greek word for correct Greek is hellenismos. Maybe we shouldn’t coin a new word, but extend the meaning of the English ‘hellenism’, so that it means the same as its parent hellenismos.
Ptolemaios
From the definition in Perseus, I was under the impression that a “hellenismos” is a Greek usage, especially by a non-Greek speaker.
If by Perseus you mean LSJ (Liddell-Scott-Jones, A Greek-English Lexicon), then meaning II is exactly what I meant.
Ptolemaios
William was looking for a word that describes a property of “Greekness”, not the category of “Greekisms”. To clarify, he gave the example “This sentence doesn’t have Latinity”, and explained that he was looking for a similar word in/for Greek. “This sentence doesn’t have Hellenismos” doesn’t quite work, in my mind, given the LSJ definitions. “This sentence is not a Hellenismos” would work, but isn’t what William wants.