What is Greek grammatik for of letter?

The Greek grammar term for "of a letter" is γράμματος (grammatos), in the genitive case.

Here's how it works:

* γράμμα (gramma) means "letter" in the nominative case (the basic form of the noun).

* γράμματος (grammatos) is the genitive case, which indicates possession or belonging.

So, "of a letter" in Greek would be γράμματος.

For example, you could say:

* Το γράμμα της αγάπης (To gramma tis agapes) - "The letter of love"

* Η αξία του γράμματος (I axia tou grammatos) - "The value of the letter"