Ο αριθμός είναι εκατό.

ο is the masculine singular definite article in the nominative case. In simple terms, it means the.

So:

• ο αριθμός = the number

Greek articles change for gender, number, and case, unlike English the, which never changes.

Because αριθμός is a masculine singular noun and it is the subject of the sentence.

Greek definite articles change depending on the noun:

• ο = masculine singular nominative
• η = feminine singular nominative
• το = neuter singular nominative

Since αριθμός is masculine, the correct article is ο.

It is in the nominative case, because it is the subject of the sentence.

In Ο αριθμός είναι εκατό, the subject is the number — that is what the sentence is talking about.

The nominative is the basic dictionary form for many Greek nouns, so you will often meet αριθμός in this form first.

The ending -ος is a very common ending for masculine nouns in Greek.

So αριθμός belongs to a very common noun pattern. In the nominative singular, many masculine nouns look like this:

• ο δρόμος = the road
• ο άνθρωπος = the person / man
• ο αριθμός = the number

This does not mean every word ending in -ος is masculine, but it is a very common pattern.

είναι is the present tense form of the verb είμαι, which means to be.

Here it means is.

So:

• είμαι = I am
• είσαι = you are
• είναι = he/she/it is

In modern Greek, είναι is also used for they are, so context tells you which meaning is intended.

In this sentence, because the subject is singular (ο αριθμός), είναι means is.

Greek works very similarly to English here:

• είναι = is
• εκατό = one hundred / a hundred / hundred

So είναι εκατό literally means is one hundred.

Greek does not need an extra word in this sentence. The number word itself acts as the predicate.

Because εκατό is a numeral and, in this use, it is generally indeclinable — it does not change for gender here.

That means you use εκατό the same way regardless of whether the noun involved is masculine, feminine, or neuter.

Examples:

• ο αριθμός είναι εκατό
• η τιμή είναι εκατό
• το σύνολο είναι εκατό

In all of these, εκατό stays the same.

A natural pronunciation is:

o ari-thmós íne e-ka-TÓ

More carefully:

• Ο = o
• αριθμός = ari-thmós
• είναι = íne
• εκατό = eka-TÓ

A few pronunciation notes:

• θ sounds like th in think
• αι in είναι is pronounced like e / i in modern Greek pronunciation here; the whole word is pronounced roughly INE
• The stressed syllables are:
  • αριθμός
  • είναι
  • εκατό

The accent marks show which syllable is stressed.

So:

• αριθμός
• είναι
• εκατό

Stress is important in Greek pronunciation, and the written accent helps you know where to place it.

Notice that ο has no accent because it is a short article and not stressed in this sentence.

Yes, Greek word order is more flexible than English, but the neutral, most straightforward order here is:

• Ο αριθμός είναι εκατό.

That is the most natural way to present the sentence as a simple statement.

A different order, such as:

• Εκατό είναι ο αριθμός.

is possible, but it sounds more marked or emphatic, like It is one hundred that the number is / The number is one hundred with special focus.

So for a learner, the basic order to use is:

• subject + verb + complement

Normally, yes, in a standard sentence like this.

Greek usually uses the definite article with a noun when it is definite, just as English does with the.

So:

• Ο αριθμός είναι εκατό. = standard and natural

Without the article:

• Αριθμός είναι εκατό.

this would sound unnatural in ordinary standard Greek for this meaning.

Yes. In this kind of sentence, εκατό can correspond to English one hundred, a hundred, or simply hundred, depending on how naturally you would express it in English.

Greek does not need a separate word for one here.

So εκατό by itself already means one hundred.

That is the final sigma.

Greek has two lowercase forms of sigma:

• σ = used at the beginning or in the middle of a word
• ς = used at the end of a word

So in αριθμός, the last letter is ς because it comes at the end.

This is only a spelling rule; it is still the same letter, sigma.

Yes, in practical meaning it can.

The verb είναι literally means is, but in mathematical or factual contexts, English often uses equals where Greek still uses είναι.

So depending on context, Ο αριθμός είναι εκατό could naturally be understood as:

• The number is one hundred
• The number equals one hundred

The Greek sentence itself is still using the ordinary verb to be.