Ventus hodie saevior est quam heri.

Because saevior is the comparative form of saevus.

• saevus = savage, fierce, violent
• saevior = fiercer, more violent

The sentence is making a comparison: the wind is fiercer today than yesterday, so Latin uses the comparative form.

Latin often makes comparisons with:

• a comparative adjective: saevior
• plus quam = than

So:

• saevior = fiercer
• quam = than
• heri = yesterday

Together: fiercer than yesterday.

This is very similar to English: fiercer than yesterday.

Ventus is nominative singular.

It is nominative because it is the subject of the sentence: the wind is the thing being described as fiercer.

• ventus = the wind
• est = is

So ventus ... est means the wind is ...

Yes. Saevior agrees with ventus in number, gender, and case.

Since ventus is:

• masculine
• singular
• nominative

the adjective must also be nominative singular masculine. The form saevior can be masculine or feminine nominative singular, and here it matches masculine ventus.

They are both adverbs.

• hodie = today
• heri = yesterday

They do not change form for case, number, or gender here. They simply tell you when something is true.

So:

• hodie modifies the whole statement: today
• heri gives the point of comparison after quam: than yesterday

Because Latin, like English, often omits repeated words when the meaning is obvious.

English says:

• The wind is fiercer today than yesterday

We do not usually say:

• The wind is fiercer today than it was yesterday

Latin works the same way:

• Ventus hodie saevior est quam heri
• literally, The wind today is fiercer than yesterday

The missing idea it was is understood from the context.

Latin has no definite article and no indefinite article.

So ventus can mean:

• wind
• the wind
• sometimes even a wind

The context tells you which is most natural. In this sentence, English usually says the wind.

The word order is fairly flexible in Latin.

This sentence is:

• Ventus hodie saevior est quam heri

But Latin could also say things like:

• Hodie ventus saevior est quam heri
• Ventus saevior est hodie quam heri

The basic meaning would stay the same, though the emphasis might shift slightly.

Latin relies more on word endings than on strict word order.

In standard classical prose, est is normally included here because it is the main verb: is.

So:

• ventus ... est = the wind is ...

Sometimes Latin can omit forms of esse in certain styles, especially poetry, but in an ordinary sentence like this, keeping est is normal and clear.

With weather, saevus often means something like:

• fierce
• violent
• stormy
• rough

So saevior here does not necessarily mean more savage in a literal emotional sense. It means the wind is stronger, harsher, more violent than it was yesterday.

Quam is very commonly used with comparatives, especially in straightforward comparisons like this one.

So:

• saevior quam heri = fiercer than yesterday

Latin also has another way to express comparison: the ablative of comparison, used without quam in some sentences. But with an adverb like heri, quam is the natural construction here.

The dictionary form is based on the positive adjective:

• saevus, saeva, saevum = fierce, savage

Its comparative is:

• saevior for masculine/feminine
• saevius for neuter

So in this sentence, saevior is the nominative singular comparative form agreeing with ventus.