Η οικογένεια είναι πλούσια.

Η means the.

In this sentence, it is the feminine singular definite article, because οικογένεια (family) is a feminine singular noun.

So:

• η = the for feminine singular nouns
• οικογένεια = family

Together: η οικογένεια = the family

In Greek, grammatical gender is not the same thing as natural sex.

A noun can be:

• masculine
• feminine
• neuter

and that is just part of how the noun behaves grammatically.

Οικογένεια is a feminine noun, so words that go with it, like the article and adjective, must match that gender:

• η οικογένεια
• πλούσια οικογένεια
• η οικογένεια είναι πλούσια

English speakers often need time to get used to this, because English usually does not assign grammatical gender to nouns like family.

Because adjectives in Greek usually agree with the noun they describe in:

• gender
• number
• case

Since οικογένεια is feminine singular nominative, the adjective must also be feminine singular nominative:

• masculine: πλούσιος
• feminine: πλούσια
• neuter: πλούσιο

So:

• η οικογένεια είναι πλούσια = correct
• η οικογένεια είναι πλούσιος = wrong
• η οικογένεια είναι πλούσιο = wrong

Because πλούσια is being used as a predicate adjective after είναι (is).

In English, we also say:

• The family is rich

not

• The family is the rich

Greek works similarly here:

• Η οικογένεια είναι πλούσια.

The adjective comes after είναι and describes the subject, so it does not need its own article.

Είναι is the present-tense form of the verb είμαι (to be).

Here it means is.

So the sentence breaks down as:

• Η οικογένεια = the family
• είναι = is
• πλούσια = rich

A useful thing to know is that είναι is also used for they are in Modern Greek, so the same form can cover both singular and plural third person depending on context.

Normally, no. In standard Greek, you usually keep the verb είναι in sentences like this.

So you say:

• Η οικογένεια είναι πλούσια.

not normally:

• Η οικογένεια πλούσια.

Leaving it out would sound incomplete in ordinary standard Greek.

Yes, Greek word order is more flexible than English, although Η οικογένεια είναι πλούσια is the most neutral and straightforward version.

You may also hear different orders for emphasis, for example:

• Πλούσια είναι η οικογένεια.
  This puts more focus on rich.

But for a learner, the safest default is:

• Subject + είναι + adjective
• Η οικογένεια είναι πλούσια.

A simple learner-friendly pronunciation is:

ee ee-ko-YEH-nya EE-ne PLOO-sya

A few notes:

• Η sounds like ee
• οικογένεια is roughly ee-ko-YEH-nya
• είναι is roughly EE-ne
• πλούσια is roughly PLOO-sya

The exact sounds are a little different from English, but that approximation is good enough to start with.

The accent marks show which syllable is stressed.

In this sentence:

• οικογένεια → stress on YE
• είναι → stress on EE
• πούσια → stress on PLOO

The article η has no accent because it is a very short function word and does not need one here.

Learning the written stress is important in Greek, because stress placement is part of the correct pronunciation.

Yes. In this adjective pattern, the feminine form often ends in -α.

For πλούσιος (rich), the common forms are:

• πλούσιος = masculine
• πλούσια = feminine
• πλούσιο = neuter

So the -α here is a normal feminine adjective ending.

This is a very common pattern in Greek, and you will see it with many adjectives.

The subject η οικογένεια is in the nominative case, because it is the subject of the sentence.

The adjective πλούσια is also in the nominative, because predicate adjectives after είμαι usually match the subject.

So grammatically:

• η οικογένεια = feminine singular nominative
• πλούσια = feminine singular nominative

That matching is one of the core agreement patterns in Greek.

Yes. Greek forms can sometimes look the same in different grammatical roles.

Πλούσια here is feminine singular to match οικογένεια, but the same form can also be neuter plural in other contexts.

For example, in another sentence, πλούσια might describe a neuter plural noun.

So when you see a form like πλούσια, you use the surrounding words to understand its role. In this sentence, because οικογένεια is feminine singular, the meaning is clearly feminine singular rich.

Grammatically, yes, because μια means a/an for feminine nouns:

• μια οικογένεια = a family

But it changes the meaning:

• Η οικογένεια είναι πλούσια. = The family is rich.
• Μια οικογένεια είναι πλούσια. = A family is rich.

The second sentence is possible, but it usually sounds less natural unless you are talking about one unspecified family in a larger context.