Η αδερφή μου λύνει προσεκτικά τον κόμπο, γιατί το λουρί ήταν πολύ σφιχτό.

These are definite articles—the Greek equivalents of the—and they change according to gender, number, and case.

In this sentence:

• η αδερφή μου = my sister
  
  • η is the feminine nominative singular article
• τον κόμπο = the knot
  
  • τον is the masculine accusative singular article
• το λουρί = the strap/leash
  
  • το is the neuter nominative/accusative singular article

So unlike English the, Greek articles change form depending on the noun’s grammatical role.

In Greek, possessive words like μου (my) are very commonly placed after the noun.

So:

• η αδερφή μου = my sister
• literally: the sister my

This is the normal Greek pattern for simple possession.

Other examples:

• το βιβλίο μου = my book
• ο φίλος μου = my friend

So even though English says my sister, Greek usually says the sister my.

Yes. Αδερφή is a very common Modern Greek form meaning sister.

You may also see:

• αδελφή

Both mean sister. In general:

• αδερφή is very common in everyday speech
• αδελφή may sound a bit more formal, conservative, or traditional in some contexts

So learners should recognize both.

Λύνει is the 3rd person singular present form of the verb λύνω.

That means it corresponds to:

• he/she/it unties
• he/she/it is untying

In this sentence, the subject is η αδερφή μου, so:

• Η αδερφή μου λύνει... = My sister unties / is untying...

Greek present tense often covers both the English simple present and present progressive, depending on context.

No. Λύνω has a broader meaning than just untie.

Depending on context, it can mean things like:

• untie
• loosen
• release
• solve (for example, a problem or exercise)

Here, because the object is τον κόμπο (the knot), the meaning is clearly untie.

So Greek often relies on context to narrow down the exact English translation.

Because κόμπος is the direct object of the verb λύνει.

The dictionary form is:

• ο κόμπος = the knot
  nominative

But after a transitive verb like λύνω, the direct object usually goes into the accusative:

• τον κόμπο

So the change is:

• ο κόμπος → τον κόμπο

This is very common with masculine nouns ending in -ος:

• ο άνθρωπος → τον άνθρωπο
• ο δρόμος → τον δρόμο

Exactly. This is a case ending change.

The noun is masculine and ends in -ος in the nominative singular:

• ο κόμπος

In the accusative singular, that ending typically becomes -ο:

• τον κόμπο

So both the article and the noun change to show that it is the direct object.

Προσεκτικά is an adverb, meaning carefully.

It describes how the action is done:

• λύνει προσεκτικά = unties carefully

Unlike adjectives, adverbs do not agree with nouns in gender, number, or case, so προσεκτικά stays the same.

Compare:

• προσεκτικός = careful (masculine adjective)
• προσεκτική = careful (feminine adjective)
• προσεκτικό = careful (neuter adjective)
• προσεκτικά = carefully (adverb)

Yes, γιατί can mean both:

• because
• why

In this sentence, it means because:

• ..., γιατί το λουρί ήταν πολύ σφιχτό.
• ..., because the strap was very tight.

Greek speakers tell the difference from context, and in writing punctuation also helps.

Compare:

• Γιατί έφυγες; = Why did you leave?
• Έφυγα γιατί νύσταζα. = I left because I was sleepy.

So this is normal and very common in Greek.

Because the sentence combines:

• a current action: η αδερφή μου λύνει...
• a past state/reason: γιατί το λουρί ήταν πολύ σφιχτό

So the idea is something like:

• she is untying the knot now,
• because the strap was very tight

Greek, like English, can mix tenses when that fits the situation. The reason may refer to an earlier state that led to the present action.

Ήταν is the imperfect form of είμαι (to be), used for he/she/it was.

So:

• το λουρί ήταν = the strap was

The imperfect is often used for:

• background description
• ongoing past states
• situations in the past

Here it describes the condition of the strap in the past: it was very tight.

Because πολύ here means very, and in that use it is an adverb, so it does not agree with the noun.

• πολύ σφιχτό = very tight

But σφιχτό is an adjective, and it does agree with το λουρί, which is neuter singular.

So:

• το λουρί = neuter singular
• σφιχτό = neuter singular adjective form

Important distinction:

• πολύ = very / much as an adverb
• πολλή / πολύς / πολύ = forms of the adjective meaning much/many, depending on grammar

In this sentence, πολύ means very, so it stays πολύ.

Because it describes το λουρί, and adjectives in Greek must agree with the noun they describe.

Since:

• λουρί is neuter singular

the adjective must also be neuter singular:

• σφιχτό

If the noun were different, the adjective would change too:

• ο κόμπος ήταν σφιχτός = the knot was tight
• η ζώνη ήταν σφιχτή = the belt was tight
• το λουρί ήταν σφιχτό = the strap was tight

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

For example, προσεκτικά could often move:

• Η αδερφή μου λύνει προσεκτικά τον κόμπο
• Η αδερφή μου λύνει τον κόμπο προσεκτικά

Both are possible, though the emphasis may shift slightly.

What is less flexible is the basic grammar:

• the articles still need to match the nouns
• the object still needs the accusative
• μου still normally follows the noun in this kind of phrase

So Greek allows movement for style or emphasis, but not random movement.

Because γιατί το λουρί ήταν πολύ σφιχτό is a reason clause: it explains why the action happened.

Greek punctuation here works much like English:

• main clause + comma + reason clause

So:

• Η αδερφή μου λύνει προσεκτικά τον κόμπο, γιατί το λουρί ήταν πολύ σφιχτό.

The comma helps separate the explanation from the main statement.