Ο ναύλος είναι ακριβός.

Ο is the masculine singular form of the.

It is used because ναύλος is a masculine singular noun, so the article must match it in gender, number, and case.

So:

• ο ναύλος = the fare

Ναύλος means fare or transport charge. In everyday contexts, it often refers to the price for traveling by ship, ferry, plane, or other transport.

It is not exactly the same as εισιτήριο, which means ticket.

So:

• ναύλος = the fare / the price of transport
• εισιτήριο = the ticket itself

In Greek, every noun has a grammatical gender: masculine, feminine, or neuter.

Ναύλος is simply a masculine noun, so it takes:

• the masculine article ο
• the masculine adjective form ακριβός

This is grammatical gender, so it does not mean the fare is somehow male. It is just how the noun behaves in Greek grammar.

Είναι means is here.

It is the present-tense form of είμαι = to be.

A useful thing to know is that είναι can mean both:

• he/she/it is
• they are

In this sentence, because the subject is singular (ο ναύλος), it means is.

Because it must agree with ναύλος.

Since ναύλος is:

• masculine
• singular
• nominative

the adjective also appears in the masculine singular nominative form:

• ακριβός = expensive

Compare:

• ο ναύλος είναι ακριβός = the fare is expensive
• η τιμή είναι ακριβή = the price is expensive/high
• το εισιτήριο είναι ακριβό = the ticket is expensive

So the ending changes depending on the noun it describes.

No. Ακριβός can also mean exact or precise, depending on context.

For example:

• ακριβή ώρα = exact time
• ακριβής περιγραφή = precise description

But in Ο ναύλος είναι ακριβός, the meaning is clearly expensive.

Because ακριβός is a predicate adjective after είναι.

In English, we also say:

• The fare is expensive

not

• The fare is the expensive

Greek works the same way here. The article goes with the noun ναύλος, not with the adjective ακριβός.

Yes. Greek word order is more flexible than English.

The neutral, standard order is:

• Ο ναύλος είναι ακριβός.

But you may also hear:

• Είναι ακριβός ο ναύλος.
• Ακριβός είναι ο ναύλος.

These versions are grammatical, but they can shift the emphasis a little. The original sentence is the most straightforward way to say it.

A rough English-style pronunciation is:

o NAV-los EE-ne a-kree-VOS

A few helpful notes:

• ναύλος is pronounced NAV-los
• είναι is pronounced EE-ne
• ακριβός is pronounced a-kree-VOS

Also, the letter combination αυ in ναύλος is pronounced av here, because it comes before the voiced consonant λ.

The accent marks show which syllable is stressed.

So:

• ναύλος → stress on the first syllable
• είναι → stress on the first syllable
• ακριβός → stress on the last syllable

Stress is important in Greek pronunciation, so the accent marks are not optional in normal writing.

In normal Greek, that would sound unnatural.

Greek usually wants the article with a definite singular noun in a sentence like this, so:

• Ο ναύλος είναι ακριβός. = natural

Without the article, it does not sound like a normal basic sentence.

If you wanted a more general statement, Greek would more naturally say something like:

• Οι ναύλοι είναι ακριβοί. = fares are expensive

The adjective and article would change to match the noun.

For example:

• Η τιμή είναι ακριβή. = the price is expensive/high
• Το εισιτήριο είναι ακριβό. = the ticket is expensive

So this sentence is a good example of an important Greek rule: articles and adjectives must agree with the noun.