Ο αιώνας τελείωσε.

Ο is the definite article and here it means the.

More specifically:

• ο = masculine, singular, nominative
• so ο αιώνας = the century

Greek uses the definite article very often, and with a specific noun like this, it is the normal form.

Αιώνας is in the nominative singular, which is the form typically used for the subject of the sentence.

You can tell because:

• the article is ο, which is nominative masculine singular
• the noun form αιώνας matches that
• the verb τελείωσε is 3rd person singular, so it agrees with a singular subject

So ο αιώνας is the subject: the century.

The dictionary form is ο αιώνας.

Greek nouns are normally learned together with their article, because the article helps you remember:

• the noun’s gender
• its usual nominative singular form

So you would usually learn it as ο αιώνας, not just αιώνας by itself.

Τελείωσε is the 3rd person singular aorist form of τελειώνω.

In this sentence it means:

• ended
• finished
• in context, came to an end

So grammatically, it is a past tense form referring to a completed event.

The aorist is used here because the sentence presents the event as a completed whole.

So Ο αιώνας τελείωσε treats the ending of the century as:

• a single completed fact
• something that is now over

That is exactly the kind of situation where Greek commonly uses the aorist.

Yes. Τελειώνω can be used both:

• intransitively: to end / to be over
• transitively: to finish something

So τελείωσε can mean:

• it ended / it was over
• or, in another context, he/she/it finished

In Ο αιώνας τελείωσε, since the subject is ο αιώνας, the natural meaning is the century ended.

Yes. Greek word order is more flexible than English.

You could also say:

• Τελείωσε ο αιώνας.

That would still mean the same thing, but the emphasis may shift slightly.

• Ο αιώνας τελείωσε sounds more neutral, with the subject stated first.
• Τελείωσε ο αιώνας can sound a bit more like The century has ended with focus on the event.

Both are natural.

A simple pronunciation guide would be:

• Ο αιώνας → o e-O-nas
• τελείωσε → te-LEE-o-se

So the whole sentence is roughly:

o e-O-nas te-LEE-o-se

A few useful notes:

• αι is pronounced like e
• the stress in αιώνας falls on ώ
• the stress in τελείωσε falls on λεί

Not always. Αιώνας can mean:

• century
• age
• era

The exact meaning depends on context.

So while in many situations it means century, in other contexts it can refer more broadly to a historical period or age.

Because Greek often expresses in one verb form what English may express in different ways.

Τελείωσε can correspond to English translations such as:

• ended
• has ended
• is over

The exact English choice depends on context. Greek does not need a separate word like has in this sentence.

Yes: the sentence shows a basic and very important Greek pattern:

• subject: ο αιώνας = masculine singular
• verb: τελείωσε = 3rd person singular

So the verb agrees with the subject in number. Since αιώνας is singular, the verb is singular too.

This is a very common sentence pattern in Greek:

• article + noun + verb