What is the Greek definition of whom?

There isn't a single, direct Greek word that perfectly translates "whom" in all its grammatical contexts. The Greek equivalent depends heavily on the grammatical function of "whom" in the English sentence (i.e., whether it's the object of a verb, preposition, or another noun).

To illustrate:

* If "whom" is the direct object: You'd use the accusative case of the appropriate pronoun. For example, "Whom did you see?" would translate to something like "τίνα εἶδες;" (tina eides;). Here, τίνα (tina) is the accusative singular masculine of "who." The gender and number of the pronoun would change depending on the person being referred to.

* If "whom" is the object of a preposition: You'd use the appropriate case governed by the preposition. For example, "To whom did you give the book?" would use the dative case. A possible translation might be: "Ὧι ἔδωκας τὸ βιβλίον;" (Hoi edōkas to biblion;). Here, ᾧ (hoi) is the dative singular masculine of "who." Again, the form would adjust based on gender and number.

In short, there's no single word. The Greek equivalent of "whom" is determined by its grammatical role in the sentence and requires selecting the correct case of a relative or interrogative pronoun (like ὅς, ἥ, ὅ, or τίς, τί).