Море шумить голосніше, ніж річка, а ввечері хвилі стають холоднішими.

Шумить comes from шуміти, meaning to make noise, to шум, to rustle, to roar, or to sound loudly, depending on context.

With море it usually means something like:

• the sea is noisy
• the sea roars
• the sea makes a louder sound

So in this sentence, Море шумить голосніше is not about speaking with a voice. It means the sea sounds louder / makes more noise.

Голосніше is a comparative adverb. It describes how the sea is making noise.

Base form:

• голосно = loudly

Comparative:

• голосніше = more loudly / louder

So:

• Море шумить голосно = The sea is noisy / sounds loudly
• Море шумить голосніше = The sea is louder / makes noise more loudly

In English, louder can sound like an adjective, but in Ukrainian this word is functioning as an adverb because it modifies the verb шумить.

Yes. Ukrainian has two common ways to make comparatives:

1. Synthetic comparative:
   голосно → голосніше

2. Analytic comparative:
   більш голосно = more loudly

In this sentence, голосніше is the more natural, compact choice.

So both are possible:

• Море шумить голосніше, ніж річка.
• Море шумить більш голосно, ніж річка.

But the first sounds smoother and more idiomatic.

Ніж means than in comparisons.

So:

• голосніше, ніж річка = louder than the river

This is the standard way to compare two things in Ukrainian.

Examples:

• вищий, ніж брат = taller than his brother
• швидше, ніж учора = faster than yesterday

So in your sentence, ніж introduces the second part of the comparison.

After ніж, the compared noun is very often left in the nominative, especially in simple comparisons like this.

So:

• Море шумить голосніше, ніж річка.

literally works like:

• The sea makes more noise than the river does.

Here річка is understood as the subject of an omitted verb:

• ніж річка (шумить)

That is why nominative makes sense.

In some other comparison structures, other cases can appear, but with ніж + a full comparison idea, nominative is very common and natural.

А often translates as and, but it is not exactly the same as і.

Very roughly:

• і = and, simply linking things
• а = and / while / whereas, often with a slight contrast or shift

In your sentence:

• ..., а ввечері хвилі стають холоднішими.

This feels like:

• ..., and in the evening the waves become colder
• or even ..., while in the evening the waves become colder

So а is a very natural choice because the sentence moves to a new but related idea.

Ввечері means in the evening.

It comes historically from в + вечір, but in modern Ukrainian ввечері is normally written as one word when it means the time expression in the evening.

Compare:

• вранці = in the morning
• вдень = in the daytime
• ввечері = in the evening
• вночі = at night

So here ввечері is simply an adverb of time telling you when the waves become colder.

Хвилі is the plural of хвиля.

• singular: хвиля = wave
• plural: хвилі = waves

Since the sentence talks about waves in general, plural is used:

• хвилі стають холоднішими = the waves become colder

Also notice agreement with the verb:

• хвиля стає = the wave becomes
• хвилі стають = the waves become

After ставати / стати meaning to become, Ukrainian very often uses the instrumental case for the noun or adjective describing the new state.

So:

• стають холоднішими = become colder

Here холоднішими is the instrumental plural form of the comparative adjective.

This is very standard:

• він став щасливішим = he became happier
• вода стала холоднішою = the water became colder
• хвилі стають холоднішими = the waves become colder

You may sometimes see nominative in other patterns, but with стати / ставати + a new quality, the instrumental is the normal form learners should expect.

It has several pieces packed into one word.

Base adjective:

• холодний = cold

Comparative:

• холодніший = colder

Then it must agree with хвилі and fit the verb стають, which calls for instrumental plural here:

• nominative plural: холодніші
• instrumental plural: холоднішими

So:

• хвилі = plural
• стають = become
• therefore the describing word appears as холоднішими

It looks complicated, but the logic is:

cold → colder → in the form needed after become

All the nouns here are in fairly straightforward forms:

• Море — nominative singular
  subject of шумить

• річка — nominative singular
  the thing being compared after ніж

• хвилі — nominative plural
  subject of стають

There is no direct object in this sentence. The more complicated form is not a noun but the adjective холоднішими, which is instrumental plural.

Both commas are standard.

1. Before ніж
   In a comparison like this, a comma is normally used:

   • Море шумить голосніше, ніж річка.

2. Before а
   А joins two clauses, so a comma is also needed:

   • ..., а ввечері хвилі стають холоднішими.

So the punctuation is completely normal for Ukrainian.

Yes. Ukrainian word order is flexible, although the original version is natural and neutral.

Original:

• Море шумить голосніше, ніж річка, а ввечері хвилі стають холоднішими.

Possible variations:

• Ввечері хвилі стають холоднішими, а море шумить голосніше, ніж річка.
• Море голосніше шумить, ніж річка...

The meaning stays similar, but the emphasis changes.

For a learner, the given word order is a good default because it sounds natural and clear.

In the present tense, Ukrainian usually does not use a separate word for am/is/are the way English does.

So Ukrainian often says:

• Він щасливий = He is happy
• Море шумить голосніше = The sea is louder / makes more noise
• Хвилі стають холоднішими = The waves become colder

The sentence does not need a present-tense є here. That is normal Ukrainian grammar.

A helpful pronunciation guide is:

• мо́ре
• шуми́ть
• голосні́ше
• рі́чка
• вве́чері
• хви́лі
• стаю́ть
• холодні́шими

A common learner difficulty is keeping the stress on:

• голосні́ше
• холодні́шими

If you want to sound natural, it helps to practice the sentence in chunks:

• Мо́ре шуми́ть голосні́ше, ніж рі́чка,
• а вве́чері хви́лі стаю́ть холодні́шими.