Η αδερφή μου θέλει να μαθαίνει καινούριες λέξεις κάθε μέρα, αλλά απόψε θέλει να μάθει μόνο αυτές τις δέκα.

In Greek, possessive pronouns like μου often come after the noun.

So:

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

This is the normal Greek pattern. English says my sister, but Greek usually says something closer to the sister of me.

You will see the same pattern in many phrases:

• το βιβλίο μου = my book
• ο φίλος μου = my friend
• η μητέρα μου = my mother

Η is the feminine singular definite article, meaning the.

It matches αδερφή, which is a feminine singular noun.

So:

• η αδερφή = the sister

Greek articles change depending on gender, number, and case. Here it is:

• η = feminine singular nominative

That fits because η αδερφή μου is the subject of the sentence.

After verbs like θέλω (to want), Greek normally uses να before the next verb.

So:

• θέλει να μαθαίνει = she wants to be learning / she wants to learn regularly
• θέλει να μάθει = she wants to learn

You can think of να as introducing a subordinate verb clause, often where English uses an infinitive like to learn.

Modern Greek does not use an infinitive the way English does, so να + verb form is the normal structure.

This is one of the most important things in the sentence: it shows an aspect difference.

• να μαθαίνει = imperfective aspect
• να μάθει = perfective aspect

In this sentence, the difference is very natural:

θέλει να μαθαίνει καινούριες λέξεις κάθε μέρα

This suggests a repeated, habitual, ongoing activity:

• she wants to learn new words every day
• in the sense of be learning regularly

θέλει να μάθει μόνο αυτές τις δέκα

This points to a specific, bounded result:

• she wants to learn only these ten
• meaning master these ten specific words tonight

So the first clause is about a general habit, and the second is about a specific completed goal.

Both exist.

• αδερφή is very common in everyday Modern Greek.
• αδελφή is also correct and may sound a bit more formal or conservative.

The same happens with:

• αδερφός / αδελφός = brother

A learner will hear αδερφή very often in normal speech.

Because the adjective καινούριες (new) has to agree with the noun λέξεις (words).

Here, λέξεις is:

• feminine
• plural
• accusative

So the adjective must match it:

• καινούριες λέξεις = new words

This agreement is normal in Greek: adjectives change form to match the noun.

You may also see a very similar form:

• καινούργιες λέξεις

Both are common and mean the same thing.

Λέξεις is the plural form of λέξη (word).

Here it is the direct object of μαθαίνει / μάθει, so it is in the accusative plural.

For this noun, the nominative plural and accusative plural look the same:

• singular: λέξη
• plural: λέξεις

So even though the case is accusative here, the form is still λέξεις.

Κάθε means every or each, and it is normally followed directly by the noun.

So:

• κάθε μέρα = every day

You do not put η here.

Other examples:

• κάθε εβδομάδα = every week
• κάθε χρόνο = every year

This is just the standard structure.

Απόψε means tonight.

It refers specifically to the evening/night of the current day.

So the contrast is:

• κάθε μέρα = every day in general
• απόψε = tonight, this specific evening

That helps create the contrast in the sentence:

• usually: she wants to learn new words every day
• but tonight: she wants to learn only these ten

Greek often repeats the verb when there is a clear contrast, and here it sounds natural:

• θέλει να μαθαίνει ... αλλά απόψε θέλει να μάθει ...

This repetition helps mark the shift from:

• a general preference or habit to
• a specific goal for tonight

Could Greek sometimes avoid repetition in other contexts? Yes. But in this sentence, repeating θέλει να is very normal and stylistically clear.

They do different jobs.

αλλά

means but

• it links two contrasting parts of the sentence

μόνο

means only

• it limits what follows

So:

• αλλά = introduces the contrast
• μόνο αυτές τις δέκα = says the limit is just these ten

Together they mean something like:

• but tonight she wants to learn only these ten

Because αυτές means these, and it points to specific items.

So:

• δέκα = ten
• αυτές τις δέκα = these ten

The noun λέξεις is understood from earlier, so Greek does not need to repeat it.

In full, it would be:

• αυτές τις δέκα λέξεις = these ten words

But since λέξεις has already been mentioned, leaving it out is completely natural.

Because αυτές is the demonstrative (these) and τις is the article used with the number phrase.

The full phrase is:

• αυτές τις δέκα λέξεις

This is a very normal Greek structure for these ten words.

Breakdown:

• αυτές = these
• τις = feminine plural accusative article
• δέκα = ten
• λέξεις = words

Greek often keeps the article in such phrases where English would not.

It is in the accusative feminine plural, because it refers to the direct object: these ten words.

Even though λέξεις is omitted, the phrase still agrees with that understood noun.

So the grammar is based on:

• λέξεις = feminine plural
• direct object = accusative

That is why we get:

• αυτές τις δέκα (λέξεις)

It could, but the meaning would change.

If you said:

• θέλει να μάθει καινούριες λέξεις κάθε μέρα

that can still mean she wants to learn new words every day, and it is not wrong. But να μαθαίνει emphasizes the repeated, habitual process more clearly.

So the original sentence is carefully chosen:

• να μαθαίνει = general ongoing habit
• να μάθει = specific result tonight

That contrast is elegant and very Greek.

Greek word order is more flexible than English word order, but the original version is very natural.

The sentence as given:

• Η αδερφή μου θέλει να μαθαίνει καινούριες λέξεις κάθε μέρα, αλλά απόψε θέλει να μάθει μόνο αυτές τις δέκα.

sounds neutral and clear.

Some parts could move for emphasis, especially απόψε or μόνο, but changing the order would usually change the focus slightly.

For example:

• αλλά θέλει απόψε να μάθει μόνο αυτές τις δέκα
• αλλά απόψε μόνο αυτές τις δέκα θέλει να μάθει

These are possible, but the original is the most straightforward for a learner.

It most often means to learn, but it can also mean to find out in some contexts.

Examples:

• Μαθαίνω ελληνικά. = I am learning Greek.
• Το έμαθα χθες. = I found out yesterday.

In your sentence, it clearly means learn because the object is words:

• μαθαίνει καινούριες λέξεις
• μάθει μόνο αυτές τις δέκα

So here there is no ambiguity.

The stress marks are important because they show which syllable is stressed.

A few useful ones here:

• αδερφή
• θέλει
• μαθαίνει
• καινούριες
• λέξεις
• απόψε
• μάθει
• αυτές

The stress can change between related forms, so it is worth learning words together with their accent. In Greek, stress is not optional spelling decoration; it is a real part of the word.