Nadchodzi zima.

Nadchodzi is a verb. It is the 3rd person singular present tense form of nadchodzić.

So literally, it means something like:

• is approaching
• is coming
• comes near

Because zima is singular, the verb is also singular: nadchodzi.

Because zima is the subject of the sentence.

In Nadchodzi zima, the thing that is approaching is winter, so zima stays in the nominative case, which is the dictionary form.

Compare:

• Zima nadchodzi. = Winter is coming.
• Nie lubię zimy. = I don't like winter.
  Here zimy is not the subject, so the form changes.

Polish does not have articles like a or the.

So zima can mean:

• winter
• the winter

The exact meaning depends on context. In this sentence, English usually translates it as Winter is coming or The winter is coming, but natural English would normally just say Winter is coming.

Yes, that is a very natural translation.

More literally, nadchodzi suggests approaching or coming nearer, so the sentence has the sense of:

• Winter is approaching
• Winter is coming

So the Polish sentence is idiomatic and natural, not just a word-for-word construction.

Yes. Zima nadchodzi is also correct.

Polish word order is more flexible than English. Both sentences are grammatical:

• Nadchodzi zima.
• Zima nadchodzi.

The difference is mainly in focus or style:

• Nadchodzi zima sounds a bit like Winter is coming / Here comes winter
• Zima nadchodzi puts more emphasis on winter

In many contexts, both work.

This is very normal in Polish.

The present tense can be used for something that is already beginning, approaching, or on its way. So nadchodzi does not mean a distant future like will come. It means something more like:

• is on the way
• is approaching now
• is about to arrive

So even though winter is not fully here yet, the process of it coming has already started.

Nadchodzić is imperfective.

That fits its meaning well, because it describes an ongoing process: winter is approaching.

Its perfective partner is usually nadejść.

For example:

• Zima nadchodzi. = Winter is approaching.
• Zima nadeszła. = Winter has arrived / Winter came.

So:

• nadchodzić = the approach is in progress
• nadejść = the arrival is completed

Yes. It is historically related.

• chodzić usually means to walk, to go around, or sometimes to go regularly
• nadchodzić means to approach, to come nearer

The prefix nad- changes the meaning. In this verb, you should learn nadchodzić as a whole word, because its meaning is not just simple walk + prefix in a literal everyday sense.

A simple learner-friendly pronunciation guide would be:

nad-CHO-djee ZEE-ma

A few notes:

• ch sounds like the h in Bach or Scottish loch
• dzi sounds roughly like jee, but softer
• zima is pronounced ZEE-ma
• Polish stress is usually on the second-to-last syllable:
  • nadCHOdzi
  • ZIma

It can be both.

In normal everyday use, Nadchodzi zima can simply mean:

• the weather is changing
• winter is getting close

But it can also sound a bit literary, dramatic, or atmospheric, depending on context.

Other common everyday alternatives include:

• Zbliża się zima. = Winter is getting closer / Winter is approaching.
• Idzie zima. = Winter is coming.
  This one is quite common and conversational.

They are very similar, and both can mean Winter is approaching.

A rough difference is:

• Nadchodzi zima = Winter is coming / approaching
• Zbliża się zima = Winter is getting closer

Nadchodzi can sound a bit more direct or vivid.
Zbliża się emphasizes the idea of coming nearer.

In many situations, they are interchangeable.

Yes.

Just like in English, winter can suggest:

• hardship
• darkness
• difficult times
• the end of a pleasant period

So Nadchodzi zima can be literal, but in the right context it can also feel symbolic or poetic.