Το μουστάκι του είναι πιο μεγάλο τώρα.

Because μουστάκι is a noun, and Greek usually uses the definite article much more often than English does.

• το = the for a neuter singular noun
• μουστάκι = moustache

So το μουστάκι literally means the moustache.

In English, we might say His moustache is bigger now, without thinking much about the article. In Greek, using the article here is normal and expected.

In Greek, possession is often expressed with a weak pronoun placed after the noun.

So:

• το μουστάκι του = his moustache
• literally: the moustache of him

This is very common Greek structure. English puts the possessive before the noun (his moustache), but Greek often uses:

• article + noun + possessive pronoun

Examples:

• το σπίτι μου = my house
• η φίλη σου = your friend
• το αυτοκίνητό τους = their car

In this sentence, του means his, but by itself του can have more than one use in Greek.

It can mean:

• his
• of him
• sometimes to him, depending on the sentence

Here, because it follows a noun and shows possession, it means his:

• το μουστάκι του = his moustache

Context tells you which meaning is intended.

Because μεγάλο has to agree with μουστάκι, which is neuter singular.

Greek adjectives change form depending on the gender and number of the noun:

• masculine: μεγάλος
• feminine: μεγάλη
• neuter: μεγάλο

Since το μουστάκι is neuter singular, the adjective must also be neuter singular:

• το μουστάκι είναι μεγάλο

In your sentence, it becomes:

• πιο μεγάλο = bigger / more big

Yes, literally it is more big, and that is a normal way to form the comparative in Greek.

• πιο = more
• μεγάλο = big
• πιο μεγάλο = bigger

This works like English more beautiful, more interesting, etc., except in Greek it is very common even with adjectives where English prefers -er.

So:

• πιο μεγάλο = bigger

Yes. Both are correct.

You can say:

• Το μουστάκι του είναι πιο μεγάλο τώρα.
• Το μουστάκι του είναι μεγαλύτερο τώρα.

Both mean His moustache is bigger now.

Very roughly:

• πιο μεγάλο = analytic comparative (more big)
• μεγαλύτερο = single-word comparative (bigger)

In everyday Greek, πιο + adjective is extremely common.

είναι is the present tense of to be for he/she/it is and also they are, depending on context.

Here it means is:

• Το μουστάκι του είναι πιο μεγάλο τώρα.
• His moustache is bigger now.

So the structure is:

• Το μουστάκι του = subject
• είναι = is
• πιο μεγάλο = bigger
• τώρα = now

Τώρα means now, and Greek word order is fairly flexible.

At the end is very natural:

• Το μουστάκι του είναι πιο μεγάλο τώρα.

But you could also hear:

• Τώρα το μουστάκι του είναι πιο μεγάλο.
• Το μουστάκι του τώρα είναι πιο μεγάλο.

The end position is common because it gives a natural emphasis to now as the new situation.

Yes, μουστάκι is a neuter noun.

One clue is its ending: many Greek neuter nouns end in -ι, though not all nouns ending in -ι behave identically. The article confirms it:

• το μουστάκι

Since the dictionary form is learned with its article, it is best to memorize nouns like this:

• το μουστάκι = moustache
• το σπίτι = house
• το παιδί = child

Learning the article together with the noun helps you remember gender.

Because plain possession is enough. Greek normally just says:

• το μουστάκι του = his moustache

You would only add something like δικό του if you wanted extra emphasis or contrast:

• το δικό του μουστάκι = his own moustache / his moustache (not someone else’s)

In your sentence, there is no need for that extra emphasis.

Yes. The sentence implies a comparison with an earlier time.

So πιο μεγάλο τώρα means:

• bigger now
• implicitly: than before

Greek often leaves the second part unstated when it is obvious from context, just like English does.

So the sentence naturally means:

• His moustache is bigger now (than it was before).

A simple pronunciation guide would be:

To moo-STA-kee too EE-ne pyo meh-GHA-lo TO-ra

A few notes:

• stress falls on στά in μουστάκι
• του here sounds like too
• πιο is usually pronounced roughly like pyo
• γ before α in μεγάλο is a soft Greek g/gh sound, not exactly like English g

So the rhythm is:

To moo-STA-kee too EE-ne pyo meh-GHA-lo TO-ra