Το διπλανό διαμέρισμα είναι άδειο τώρα.

Το is the definite article here, meaning the.

Greek articles change for gender, number, and case.
Since διαμέρισμα (apartment) is neuter singular, the correct article is το.

So:

• το διαμέρισμα = the apartment

In this sentence, το goes with the whole noun phrase:

• το διπλανό διαμέρισμα = the next-door / neighboring apartment

Διπλανό is an adjective meaning next-door, neighboring, adjacent.

It changes form to match the noun it describes. Since διαμέρισμα is:

• neuter
• singular
• nominative (the subject of the sentence)

the adjective must also be neuter singular nominative:

• masculine: διπλανός
• feminine: διπλανή
• neuter: διπλανό

So:

• το διπλανό διαμέρισμα = the neighboring apartment

Because Greek nouns have grammatical gender, and διαμέρισμα happens to be a neuter noun.

This does not mean the apartment is somehow “neutral” in meaning. It is just a grammatical category. In Greek, every noun belongs to a gender class, and adjectives/articles must agree with it.

So with διαμέρισμα, you use neuter forms such as:

• το = the
• διπλανό = neighboring
• άδειο = empty

Because άδειο has to agree with διαμέρισμα, which is neuter singular.

The adjective άδειος means empty or vacant, and its forms are:

• masculine: άδειος
• feminine: άδεια
• neuter: άδειο

Since the subject is το διπλανό διαμέρισμα, the adjective after είναι also appears in the neuter singular:

• Το διαμέρισμα είναι άδειο. = The apartment is empty.

Because άδειο is not being used as part of the noun phrase; it is a predicate adjective after the verb είναι (is).

Compare:

• το άδειο διαμέρισμα = the empty apartment

  • here άδειο directly describes the noun inside the noun phrase

• το διαμέρισμα είναι άδειο = the apartment is empty

  • here άδειο comes after is and functions like empty in English

So no article is needed before άδειο.

Είναι is the 3rd person singular form of είμαι, meaning to be.

Here it means is:

• είμαι = I am
• είσαι = you are
• είναι = he/she/it is

So:

• Το διπλανό διαμέρισμα είναι άδειο.
  = The neighboring apartment is empty.

Also, in modern Greek, είναι can mean both is and are, depending on the subject.

Τώρα means now.

Putting it at the end is very natural in Greek:

• Το διπλανό διαμέρισμα είναι άδειο τώρα.

But Greek word order is often more flexible than English, so you may also hear:

• Τώρα το διπλανό διαμέρισμα είναι άδειο.
• Το διπλανό διαμέρισμα τώρα είναι άδειο.

These all mean roughly the same thing, though the emphasis can shift slightly.

Ending with τώρα often feels like a natural way to add the time information after the main statement.

Often yes, but its meaning is a little broader than the English phrase next-door.

Διπλανός / διπλανό can mean:

• next
• adjacent
• neighboring
• next-door

So το διπλανό διαμέρισμα could be understood as:

• the apartment next door
• the neighboring apartment
• the adjacent apartment

The exact best translation depends on context.

Usually not in a normal sentence like this.

Greek uses the definite article very regularly. If you are talking about the neighboring apartment, you normally say:

• Το διπλανό διαμέρισμα...

Omitting το would sound incomplete or unnatural in standard usage, unless you were speaking in a special context such as notes, labels, headlines, or very telegraphic speech.

The dictionary forms are:

• ο διπλανός / η διπλανή / το διπλανό = neighboring, next-door
• το διαμέρισμα = apartment
• είμαι = to be
• ο άδειος / η άδεια / το άδειο = empty, vacant
• τώρα = now

This is useful because adjectives and verbs often appear in changed forms inside sentences, so learners need the dictionary form to look them up.

A rough pronunciation guide is:

To diplanó diamérisma íne ádio tóra

A few notes:

• δι in διπλανό sounds like thee with a voiced th-type sound? Actually in modern Greek δ is like the th in this, so δι is closer to thi in this + ee
• γ does not appear here, so that part is easier
• stress matters a lot in Greek:
  • διπλανό
  • διαμέρισμα
  • είναι
  • άδειο
  • τώρα

If you want a more learner-friendly approximation:

to thip-la-NO thia-ME-ri-sma EE-ne A-thyo TO-ra

That is only approximate, but it helps show the stress.

Yes.

In this sentence, άδειο could mean:

• physically empty
• vacant / unoccupied

So if you are talking about an apartment, άδειο often implies:

• nobody is living there now
• it is unoccupied
• it may also be unfurnished or unused, depending on context

English chooses between empty and vacant depending on the situation, but Greek often uses άδειο for both ideas.