Η επιλέξιμη κατοικία είναι κύρια κατοικία.

It has three main parts:

Η επιλέξιμη κατοικία = the subject
είναι = the verb, is
κύρια κατοικία = the complement after είναι

So the structure is:

[article + adjective + noun] + [verb] + [adjective + noun]

Both noun phrases are about κατοικία, so the sentence is describing what kind of residence the eligible residence is.

Η is the feminine singular definite article, meaning the.

It is used because κατοικία is a feminine singular noun. In Greek, the article must agree with the noun in gender, number, and case.

So:

• η κατοικία = the residence
• not ο κατοικία or το κατοικία

Because adjectives in Greek agree with the noun they describe.

Here, both επιλέξιμη and κύρια describe κατοικία, which is:

• feminine
• singular
• nominative

So the adjectives must also be feminine singular nominative.

For example:

• επιλέξιμος = masculine
• επιλέξιμη = feminine
• επιλέξιμο = neuter

and

• κύριος = masculine
• κύρια = feminine
• κύριο = neuter

A useful extra note: κύρια here means main/principal. It is different from κυρία, which means lady / Mrs. The accent changes the meaning.

In formal or administrative Greek, repeating the noun is very common because it keeps the meaning precise.

So Η επιλέξιμη κατοικία είναι κύρια κατοικία is clear and explicit.

If the context were already very clear, Greek might sometimes avoid repetition, but here repeating κατοικία is the natural formal choice. A version like Η επιλέξιμη κατοικία είναι κύρια can sound incomplete unless the noun is already fully understood from context.

This is a very common question for English speakers.

After είναι, Greek often uses a noun phrase without an article when it is classifying or describing something.

So είναι κύρια κατοικία means that it counts as / is classified as a primary residence.

Also, Greek does not have an indefinite article like English a/an. So the absence of an article does not always map neatly to English a.

Compare:

• είναι κύρια κατοικία = it is primary residence / a primary residence in a classifying sense
• είναι η κύρια κατοικία = it is the main residence, a more definite and specific identification

The main noun phrases are in the nominative.

• Η επιλέξιμη κατοικία is nominative because it is the subject.
• κύρια κατοικία is also nominative because it comes after είναι as a predicate noun phrase.

So this sentence is a good example of Greek using the nominative on both sides of to be.

Because the subject is singular: η κατοικία = the residence.

Greek verbs agree with their subject in number and person.

So:

• η κατοικία είναι = the residence is
• οι κατοικίες είναι = the residences are

Notice that είναι is used for both singular and plural in the present tense of to be, so the subject tells you whether the meaning is singular or plural.

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

The sentence as given is the most neutral and straightforward order:

Η επιλέξιμη κατοικία είναι κύρια κατοικία.

Other orders are possible, but they usually sound more marked, more formal, or more emphatic. For a learner, the given order is the safest one to use.

A rough pronunciation guide is:

ee e-pee-LEK-see-mee ka-ti-KEE-a EE-ne KEE-ria ka-ti-KEE-a

A few helpful points:

• Η sounds like ee
• οι in κατοικία sounds like ee, not like English oi in coin
• the accent mark shows the stressed syllable:
  • επιλέξιμη
  • κατοικία
  • είναι
  • κύρια

Because κατοικία is more formal and administrative.

• κατοικία = residence, dwelling
• σπίτι = house, home in everyday speech

In legal, tax, housing, or official contexts, κύρια κατοικία is a standard phrase meaning primary/principal residence. That is why κατοικία is the natural word in this sentence.