Ο χτύπος στην πόρτα ήταν πολύ δυνατός.

Yes. Ο χτύπος means the knock, the bang, or more generally the sound of a hit/strike.

In this sentence, Ο χτύπος στην πόρτα means the knock at/on the door.

The noun χτύπος comes from the verb χτυπάω / χτυπώ, which can mean to hit, to strike, to knock, or sometimes to ring depending on context.

Because χτύπος is a masculine singular noun.

So the correct definite article is:

• ο = the for masculine singular nouns

That is why we get:

• ο χτύπος = the knock

The adjective later in the sentence also matches this masculine singular noun:

• δυνατός = masculine singular
• not δυνατή or δυνατό

Στην πόρτα literally means at the door or on the door, depending on context.

It is made from:

• σε = in / at / to / on
• την = the (feminine singular accusative)

These combine in normal Greek spelling:

• σε την → στην

So:

• στην πόρτα = at the door / on the door

In the context of knocking, English usually says on the door, but Greek commonly uses στην πόρτα.

Because after σε, Greek normally uses the accusative case.

So:

• η πόρτα = the door (nominative)
• την πόρτα = the door (accusative)

After σε, you get:

• σε την πόρτα → στην πόρτα

This is very common in Greek:

• στο σπίτι = at/to the house
• στην τάξη = in the classroom
• στον φίλο = to the friend

Ήταν is the past tense of είμαι (to be).

So:

• είναι = is
• ήταν = was

In this sentence:

• Ο χτύπος στην πόρτα ήταν πολύ δυνατός.
• The knock at the door was very loud.

Greek uses ήταν here exactly as English uses was.

Δυνατός is an adjective. Its basic meaning is strong, but depending on context it can also mean:

• loud
• powerful
• intense

Here it means loud, because it describes a knock/sound:

• πολύ δυνατός = very loud

If you used it with a person, it would more likely mean strong:

• Είναι πολύ δυνατός. = He is very strong.

So the exact translation depends on what the adjective is describing.

Because Greek is not saying the knock sounded loudly. It is describing the knock itself with an adjective.

Structure:

• Ο χτύπος ... ήταν πολύ δυνατός
• literally: The knock ... was very loud

So δυνατός agrees with χτύπος as an adjective.

If Greek were using an adverb, it would be a different structure. But here the idea is:

• the knock was loud not
• someone knocked loudly

Because πολύ here works as an adverb, meaning very.

It modifies the adjective δυνατός:

• πολύ δυνατός = very loud

When πολύ means very, it does not change form.

Compare:

• πολύ δυνατός = very loud
• πολύ καλή = very good
• πολύ μεγάλα = very big

But Greek also has adjective forms meaning much/many, and those do change:

• πολλός, πολλή, πολύ
• πολλοί, πολλές, πολλά

That is a different use.

Yes. Greek word order is more flexible than English.

The neutral order here is:

• Ο χτύπος στην πόρτα ήταν πολύ δυνατός.

But you could also hear variations such as:

• Ήταν πολύ δυνατός ο χτύπος στην πόρτα.

This changes the emphasis a bit, but the basic meaning stays the same.

Greek often moves words around for focus, style, or emphasis in a way that English usually cannot do as freely.

A rough pronunciation is:

• htee-pos

More carefully:

• χτ at the beginning can be tricky for English speakers
• ύ is stressed, so the stress is on the first syllable you really hear strongly: ΧΤΥ
• πος sounds like pos

A few notes:

• χ is not like English ch in chair
• it is more like the h-like sound in German Bach or Scottish loch
• τυ here sounds roughly like ty / tee depending on accent and speech

So χτύπος is approximately KHTEE-pos.

In this context, it can correspond to either in English.

Greek says:

• χτύπος στην πόρτα

English might say:

• a knock at the door
• a knock on the door

Both work as translations depending on style and context.

So you should not try to match σε / στην to only one English preposition every time. Greek σε is broader and often covers meanings that English splits into at, to, in, or on.

No. Χτύπος is broader than that.

It can refer to:

• a knock
• a hit
• a bang
• a beat
• a thump

For example, depending on context, it could describe:

• a knock on a door
• the sound of something hitting the floor
• a heartbeat or rhythmic beat in some uses

In this sentence, στην πόρτα makes it clear that it is a knock at/on the door.

The sentence breaks down like this:

• Ο χτύπος στην πόρτα = subject noun phrase = the knock at/on the door
• ήταν = verb = was
• πολύ δυνατός = predicate adjective phrase = very loud

So the full structure is:

• [Subject] + [was] + [description]

That is why the sentence is straightforward to translate once you recognize the parts:

• Ο χτύπος στην πόρτα ήταν πολύ δυνατός.
• The knock at the door was very loud.