Ο ειδικός περιμένει.

Ο is the masculine singular definite article, so it means the.

In this sentence, Ο matches ειδικός in:

• gender: masculine
• number: singular
• case: nominative

So Ο ειδικός means the expert or the specialist.

ειδικός here means expert or specialist.

It can be:

• an adjective in other contexts, meaning something like specialized
• a noun, as it is here, meaning expert/specialist

So in Ο ειδικός περιμένει, ειδικός is being used as a noun.

Greek uses the definite article very often, including with many nouns referring to people.

So Ο ειδικός is the normal way to say the expert.

If you removed the article and just said Ειδικός περιμένει, it would usually sound less natural in ordinary speech, unless it were a headline, label, or some very special context.

In this sentence, yes, it is masculine because of the article Ο.

A female expert can be η ειδικός.
So the noun can refer to either sex, but the article shows the gender in the sentence.

Compare:

• ο ειδικός = the male expert
• η ειδικός = the female expert

περιμένει is:

• present tense
• third person singular
• from the verb περιμένω = to wait

So it means:

• he waits
• she waits
• it waits
• or, in natural English, he/she is waiting

Greek present tense often covers both simple present and present continuous, depending on context.

Greek often leaves out subject pronouns because the verb ending already gives person and number.

So περιμένει already tells you it is third person singular.

You could say:

• Περιμένει = He/She is waiting
• Ο ειδικός περιμένει = The expert is waiting

The noun phrase ο ειδικός is included because the speaker wants to name the subject clearly.

No. περιμένω can be used without saying what someone is waiting for, if that information is unknown, obvious, or unimportant.

So Ο ειδικός περιμένει is a complete sentence and simply means that the expert is waiting.

If you want to add what the person is waiting for, you can:

• Ο ειδικός περιμένει τον πελάτη. = The expert is waiting for the client.

Yes. Greek word order is more flexible than English word order.

The neutral order here is:

• Ο ειδικός περιμένει.

But you could also say:

• Περιμένει ο ειδικός.

That still means basically the same thing, but the emphasis may shift slightly. Greek often changes word order for focus, emphasis, or style.

A rough pronunciation is:

o ee-thi-KOS pe-ri-ME-ni

More accurately:

• Ο = a short o
• ει sounds like ee
• δ sounds like the th in this
• stress in ειδικός is on the last syllable: ειδιΚΟΣ
• stress in περιμένει is on ΜΕ: περιΜΕνει

So the stress pattern is:

ο ειδιΚΟΣ περιΜΕνει

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

Here is the same noun in a few common forms:

• ο ειδικός = nominative singular, subject
• τον ειδικό = accusative singular, object
• του ειδικού = genitive singular, of the expert

So in this sentence, ο ειδικός is nominative because the expert is the one doing the waiting.