Ο απόπλους και ο κατάπλους είναι αύριο.

ο is the masculine singular definite article, so here it means the.

It appears twice because Greek often repeats the article before each noun in a list:

• ο απόπλους = the departure
• ο κατάπλους = the arrival

So ο απόπλους και ο κατάπλους is literally the departure and the arrival.

Repeating the article is very normal and natural in Greek.

Yes. You can tell because they take the article ο, which is the nominative singular article for masculine nouns.

So:

• ο απόπλους
• ο κατάπλους

Both are masculine singular nouns.

They are in the nominative case because they are the subject of the sentence.

The basic structure is:

• Ο απόπλους και ο κατάπλους = the subject
• είναι = the verb
• αύριο = tomorrow

So Greek uses the nominative here just as English uses the subject form in The departure and the arrival are tomorrow.

είναι is the present tense of to be.

So the sentence structure is simply:

• Ο απόπλους και ο κατάπλους = the departure and the arrival
• είναι = are
• αύριο = tomorrow

A useful thing to know: είναι is the same form for both he/she/it is and they are in Modern Greek. So even though the subject has two things joined by και, the verb form still stays είναι.

Because in Modern Greek, είναι serves for both:

• it is
• they are

So there is no different plural form here.

That means:

• Ο απόπλους είναι αύριο = The departure is tomorrow.
• Ο απόπλους και ο κατάπλους είναι αύριο = The departure and the arrival are tomorrow.

The verb looks the same in both sentences.

και means and.

It links the two nouns:

• ο απόπλους και ο κατάπλους
• the departure and the arrival

It is one of the most common Greek words.

Because αύριο is an adverb meaning tomorrow.

Greek often uses time adverbs directly, without a preposition:

• είναι αύριο = is/are tomorrow
• φεύγω αύριο = I leave tomorrow
• έρχεται αύριο = he/she is coming tomorrow

So this is completely normal Greek.

Yes. Greek word order is more flexible than English, although this sentence is perfectly normal as it stands.

You could also hear things like:

• Αύριο είναι ο απόπλους και ο κατάπλους.
• Ο απόπλους και ο κατάπλους αύριο είναι. (less neutral, more marked)

The original sentence is a straightforward, neutral way to say it.

Not really. These are more formal or nautical words.

They are especially used for ships, ferries, ports, and official schedules:

• απόπλους = departure, sailing out
• κατάπλους = arrival, sailing in

In more everyday Greek, depending on context, people might more often use words like:

• αναχώρηση = departure
• άφιξη = arrival

So this sentence sounds a bit technical or transport-related.

A rough pronunciation guide:

• ο = o
• απόπλους = a-PO-plous
• και = roughly ke
• ο κατάπλους = o ka-TA-plous
• είναι = EE-ne
• αύριο = AV-rio

The written accents show the stress:

• απόπλους
• κατάπλους
• είναι
• αύριο

Sometimes Greek can use one article with two coordinated nouns, but in a sentence like this, repeating the article is the most natural and safest choice:

• ο απόπλους και ο κατάπλους

That clearly treats them as two separate items: the departure and the arrival.

So for a learner, it is best to copy the version with both articles.

Yes. αύριο applies to the whole subject phrase:

• the departure and the arrival are tomorrow

So the idea is that both the departure and the arrival are scheduled for tomorrow.

Greek does not need to repeat αύριο for each item unless the speaker wants extra emphasis or clarity.