Ο αδερφός μου λέει ότι το γιλέκο είναι πρακτικό την άνοιξη, ενώ η βερμούδα είναι καλύτερη μόνο όταν έχει πολλή ζέστη.

In Greek, short possessive words like μου usually come after the noun:

• ο αδερφός μου = my brother
• η φίλη μου = my friend
• το σπίτι μου = my house

Putting μου before the noun is not the normal pattern. If you want extra emphasis, Greek often uses δικός:

• ο δικός μου αδερφός = my own brother / my brother (as opposed to someone else’s)

Yes. Both mean brother.

• αδερφός is very common in everyday Modern Greek.
• αδελφός is also correct, but can sound a bit more formal or traditional in some contexts.

A learner will hear both, so it is good to recognize both forms.

Greek uses the definite article much more often than English does. In a sentence like this, the article is completely normal:

• ο αδερφός μου
• το γιλέκο
• η βερμούδα

Even when English might say just a vest or shorts in a general sense, Greek often prefers the article. So learners should not expect article use to match English exactly.

Yes, η βερμούδα is singular in Greek, even though English usually says shorts in the plural.

So:

• η βερμούδα = shorts / a pair of shorts
• οι βερμούδες = shorts in the plural, if you mean several pairs

This is a very common difference between Greek and English vocabulary.

It is the present tense of λέω = to say.

• λέει can mean says
• depending on context, it can also mean is saying

In this sentence, says is the most natural translation because it sounds like a general opinion:

• Ο αδερφός μου λέει ότι... = My brother says that...

ότι introduces a clause meaning that:

• λέει ότι... = says that...

So the sentence structure is:

• My brother says
• that the vest is practical in spring...

A useful extra point: ότι is different from ό,τι.

• ότι = that
• ό,τι = whatever / anything that

The accenting helps distinguish them in writing.

Because πρακτικό has to agree with το γιλέκο.

• γιλέκο is neuter singular
• so the adjective must also be neuter singular
• therefore: πρακτικό

Compare:

• ο σάκος είναι πρακτικός = masculine
• η τσάντα είναι πρακτική = feminine
• το γιλέκο είναι πρακτικό = neuter

Greek adjectives change form to match the noun’s gender and number.

For the same reason: adjective agreement.

• βερμούδα is feminine singular
• so the adjective must be feminine singular
• therefore: καλύτερη

Compare the three forms:

• καλύτερος = masculine
• καλύτερη = feminine
• καλύτερο = neuter

So η βερμούδα είναι καλύτερη means the shorts are better.

Here it means better.

καλύτερος / καλύτερη / καλύτερο is the comparative form of καλός (good), so it often means better.

In this sentence, the comparison is understood from context:

• the vest is practical in spring,
• whereas the shorts are better only in very hot weather.

Greek does not always need an explicit than phrase for a comparative idea to be understood.

Here ενώ means while, whereas, or on the other hand.

It introduces a contrast:

• το γιλέκο είναι πρακτικό την άνοιξη
• ενώ η βερμούδα είναι καλύτερη μόνο όταν έχει πολλή ζέστη

So it is not mainly about two things happening at the same time. It is more about comparing or contrasting them.

In Greek, many time expressions use the accusative with the article and no preposition:

• την άνοιξη = in spring
• το καλοκαίρι = in summer
• τον χειμώνα = in winter

So την άνοιξη is a standard way to say in spring.

This is one of those places where Greek structure does not match English word-for-word.

It means only when.

• όταν = when
• μόνο = only

Together they limit the condition:

• η βερμούδα είναι καλύτερη μόνο όταν έχει πολλή ζέστη
• the shorts are better only when it’s very hot

So the idea is that the shorts are not generally the better choice; they are better specifically under that condition.

Because ζέστη is a noun, and πολλή agrees with it.

• ζέστη = heat, feminine singular
• so Greek says πολλή ζέστη = a lot of heat

That is why you get πολλή (feminine form), not πολύ.

This is different from πολύ used as an adverb:

• πολύ καλός = very good
• πολύ ζεστό = very hot

But here the structure is not very hot. It is literally more like there is a lot of heat.

This is an impersonal expression. Greek often says:

• έχει ζέστη = it is hot
• έχει κρύο = it is cold

There is no explicit subject word like English it. Greek simply uses the verb in the third person singular.

So:

• όταν έχει πολλή ζέστη = when it is very hot

Yes, αλλά could be used in some similar contexts, but ενώ is very natural here because the sentence sets up a comparison between two items.

• ενώ often sounds smoother when contrasting two parallel statements
• αλλά is a more direct but

So:

• ..., ενώ η βερμούδα... = a neat contrast between the vest and the shorts
• ..., αλλά η βερμούδα... = also possible, but slightly different in tone

In this sentence, ενώ is a good choice because the structure is balanced and comparative.