Η φίλη μου είπε ότι το βαφτιστήρι της γκρινιάζει όταν νυστάζει.

In Greek, a possessed noun is very often used with the definite article. So η φίλη μου is the normal way to say my friend.

Literally, it is closer to the friend of mine, but that is just how Greek structures it. English usually drops the article here; Greek usually keeps it.

The short possessive pronouns μου, σου, του, της, μας, σας, τους usually come after the noun they belong to:

η φίλη μου = my friend
το σπίτι της = her house

This is the standard pattern in everyday Greek.

της means her. In this sentence, it most naturally refers to η φίλη μου.

So:

το βαφτιστήρι της = her godchild

In a bigger conversation, της could in theory refer to some other woman already mentioned, but in this sentence by itself, my friend is the obvious reference.

Βαφτιστήρι is a neuter noun in Greek, so it takes το.

This is a good example of how grammatical gender and biological sex are not always the same thing. A βαφτιστήρι can be male or female, but the noun itself is grammatically neuter. Greek does this with other person-words too, such as το παιδί.

It means godchild: the child for whom someone is a godparent.

So το βαφτιστήρι της means her godchild.

Ότι introduces a reported statement. Here it works like English that:

είπε ότι... = said that...

So the sentence has:

• the main clause: Η φίλη μου είπε
• the reported content: ότι το βαφτιστήρι της γκρινιάζει όταν νυστάζει

A very common alternative is πως: Η φίλη μου είπε πως...

No.

ότι = that
ό,τι = whatever / anything that

They are different words, and the comma-like mark in ό,τι matters.

In your sentence, it is ότι because it introduces what the friend said.

Because the sentence combines two different time perspectives:

• είπε = the act of speaking happened in the past
• γκρινιάζει όταν νυστάζει = a general or habitual fact about the godchild

Greek often keeps the present tense in reported speech if the statement is still true or describes a usual pattern.

So the idea is:

My friend said [past event] that her godchild whines whenever he/she gets sleepy [general habit].

Όταν means when or whenever.

Here, όταν νυστάζει means when/whenever he or she feels sleepy. The present tense is natural because this describes a repeated situation, not one single event.

So the structure is: γκρινιάζει όταν νυστάζει = whines whenever sleepy / whenever he or she gets sleepy

No. Νυστάζει means is sleepy, feels sleepy, or is getting drowsy.

If you want is sleeping, Greek uses κοιμάται.

So:

• νυστάζει = feels sleepy
• κοιμάται = is asleep / is sleeping

It usually means something like whines, grumbles, complains, or fusses.

For a child, English often translates it best as whines or fusses. It does not necessarily mean actual crying, although crying could happen too.

So in this sentence, the feeling is that the godchild becomes irritable and starts complaining or fussing when sleepy.

Greek often leaves subject pronouns out because the verb ending already shows the person and number, and here the subject noun is already stated:

το βαφτιστήρι της γκρινιάζει

That is enough to mean her godchild whines. A separate he/she is unnecessary unless you want special emphasis or contrast.

Yes. Greek word order is more flexible than English word order.

For example, you could also say:

Η φίλη μου είπε ότι όταν νυστάζει, το βαφτιστήρι της γκρινιάζει.

That still means essentially the same thing. The original order is just a very natural, neutral way to say it.

Roughly: gree-NYA-zee

A few helpful points:

• γκ at the beginning of a word sounds like a hard g
• the stress is on -ιά-
• νιά sounds like nya

So γκρινιάζει is approximately gri-NYA-zi.