Learn Hardcore Greek: Ο αδερφός μου είναι μεγαλύτερος από εμένα.

Leaving the article out (αδερφός μου) is possible but feels incomplete or more like a label (e.g. on a family tree). In natural everyday speech you almost always say ο αδερφός μου.

What’s the difference between αδερφός and αδελφός?

They are essentially the same word: brother.

αδερφός is the most common modern, informal spelling and pronunciation.
αδελφός is more traditional/learned; you still see it in writing (books, formal texts, religious language), and some people pronounce it that way.

In everyday speech, you’ll usually hear αδερφός. Both are correct; it’s mostly a matter of style and register.

Why does μου come after αδερφός and not before, like μου αδερφός?

In Greek, unstressed possessive pronouns (my, your, his, etc.) are clitics and usually come after the noun:

ο αδερφός μου = my brother
το σπίτι σου = your house
η μητέρα του = his mother

So the normal order is:

article + noun + weak possessive pronoun

Putting μου before (μου αδερφός) sounds very strange or poetic/archaic. In normal speech, always say ο αδερφός μου, not μου ο αδερφός or μου αδερφός.

What does μεγαλύτερος literally mean? Is it “bigger” or “older”?

The adjective μεγάλος basically means big / large / great, and in the context of age it also means old / older.

μεγαλύτερος is the comparative form of μεγάλος:

μεγάλος = big / old
μεγαλύτερος = bigger / older

Which translation you choose depends on context:

Το σπίτι του είναι μεγαλύτερο. = His house is bigger.
Ο αδερφός μου είναι μεγαλύτερος. = My brother is older.

With people and age, μεγαλύτερος almost always means older.

How is μεγαλύτερος formed from μεγάλος? What are the comparative and superlative?

μεγάλος follows a regular pattern:

Positive: μεγάλος = big
Comparative: μεγαλύτερος = bigger / older
Superlative:
- ο πιο μεγάλος or ο μεγαλύτερος = the biggest

So:

Ο Γιάννης είναι μεγάλος. = John is big / grown-up.
Ο Πέτρος είναι μεγαλύτερος από τον Γιάννη. = Petros is bigger / older than John.
Ο Κώστας είναι ο μεγαλύτερος. = Kostas is the biggest / the oldest.

Could I say πιο μεγάλος instead of μεγαλύτερος? Is there a difference?

Yes, you can. Both are correct:

μεγαλύτερος
πιο μεγάλος

Meaning-wise they’re the same: bigger / older.

Nuance:

μεγαλύτερος sounds a bit more compact and is very common.
πιο μεγάλος feels a bit more informal or spoken, but it’s also very common.

In your sentence:

Ο αδερφός μου είναι μεγαλύτερος από εμένα.
Ο αδερφός μου είναι πιο μεγάλος από εμένα.

Both mean My brother is older than me.

Why is από used in a comparison? I thought από means from.

από does mean from, but in Greek it is also used to introduce the second part of a comparison, like English than.

So:

μεγαλύτερος από εμένα = older than me
καλύτερος από εσένα = better than you

So από can mean:

from: έρχομαι από την Ελλάδα = I come from Greece
than (after a comparative): είναι καλύτερος από μένα = he is better than me

Here, it clearly has the comparative meaning.

Why do we say από εμένα and not από εγώ?

After a preposition like από, Greek does not use the subject form εγώ. It uses an object / stressed form instead:

Subject: εγώ = I
Stressed object form: εμένα (or shorter μένα) = me

So you must say:

από εμένα or από μένα = than me, from me
not από εγώ.

Rule of thumb: after prepositions (σε, από, για, με, κτλ.) use εμένα/μένα, εσένα/σένα, etc., not εγώ.

What’s the difference between εμένα and μένα here?

They are two forms of the same pronoun:

εμένα = full, more emphatic
μένα = shorter, more colloquial

In your sentence:

Ο αδερφός μου είναι μεγαλύτερος από εμένα.
Ο αδερφός μου είναι μεγαλύτερος από μένα.

Both are correct and mean the same thing. από μένα is very common in everyday speech; από εμένα sounds a bit more careful or emphatic.

Could I leave out από εμένα and just say Ο αδερφός μου είναι μεγαλύτερος?

Yes, grammatically you can say:

Ο αδερφός μου είναι μεγαλύτερος.

But then the comparison is incomplete; it just says My brother is older, without saying older than who. That can still be natural if the comparison is understood from context:

(Talking about you and your brother)
– Ποιος είναι μεγαλύτερος; Who is older?
– Ο αδερφός μου είναι μεγαλύτερος. My brother is older.

If you want to clearly say older than me, it’s better to keep από εμένα / από μένα.

Is the word order flexible? Could I say Ο αδερφός μου είναι από εμένα μεγαλύτερος?

Greek word order is more flexible than English, but not every permutation sounds natural.

These are all acceptable, with slightly different emphasis:

Ο αδερφός μου είναι μεγαλύτερος από εμένα.
– Neutral, most natural.
Ο αδερφός μου είναι μεγαλύτερος από μένα.
– Same, just using μένα.
Ο αδερφός μου είναι, από μένα, μεγαλύτερος.
– Possible in speech for added emphasis, but sounds a bit marked.

Ο αδερφός μου είναι από εμένα μεγαλύτερος is not wrong, but it sounds unusual and heavy in everyday speech. Safest and most natural is:

Ο αδερφός μου είναι μεγαλύτερος από μένα / εμένα.

How would I say My sister is younger than me using the same pattern?

Use αδερφή (sister) and μικρός → μικρότερος (small → smaller / younger):

Η αδερφή μου είναι μικρότερη από μένα.
Η αδερφή μου είναι μικρότερη από εμένα.

Both mean My sister is younger than me.

Note the changes:

Η instead of Ο because αδερφή is feminine.
μικρότερη (feminine form) instead of μεγαλύτερος.

Could I say Ο αδερφός μου είναι μεγαλύτερός μου without από? Is that correct?

This form exists, but it is:

relatively formal / literary
less common in everyday modern speech

μεγαλύτερός μου uses the genitive pronoun μου instead of από εμένα for the comparison. It literally means my elder / elder to me.

So:

Ο αδερφός μου είναι μεγαλύτερός μου.
≈ Ο αδερφός μου είναι μεγαλύτερος από μένα.

In everyday spoken Greek, people almost always say:

Ο αδερφός μου είναι μεγαλύτερος από μένα / εμένα.

You can understand μεγαλύτερός μου, and you’ll see it more in writing or more formal language, but you don’t need to use it as a learner.