Ten zegar to unikat.

Because ten has to agree with zegar in gender, number, and case.

• zegar is masculine singular
• in the nominative singular, the demonstrative this is:
  • ten for masculine
  • ta for feminine
  • to for neuter

So:

• ten zegar = this clock
• ta lampa = this lamp
• to okno = this window

Not exactly. Polish does not have articles like a and the.

Ten is a demonstrative, so it means this or that specific one, depending on context. In this sentence, it points to a particular clock: this clock.

So ten is stronger and more specific than English the. It is not just a general marker of definiteness.

No. Zegar usually means a clock, especially a larger one:

• wall clock
• grandfather clock
• tower clock
• mantel clock

Zegarek usually means a watch, especially a wristwatch or small personal timepiece.

So Ten zegar to unikat is talking about a clock, not a watch.

Here, to is a linking word used to connect two noun phrases, something like is in English.

In Ten zegar to unikat, it links:

• ten zegar = the subject
• unikat = what it is being identified as

This structure is very common in Polish when one thing is being identified or classified as another thing.

So the pattern is often:

• X to Y = X is Y

Examples:

• To mój brat. = This is my brother.
• Warszawa to stolica Polski. = Warsaw is the capital of Poland.

Because after to, Polish usually uses the nominative form of the noun.

So:

• Ten zegar to unikat. — correct
• Ten zegar jest unikatem. — also correct, but with jest the noun is commonly in the instrumental

This is a very useful contrast:

• X to Y → usually nominative
• X jest Y-em / Y-ą → often instrumental

So:

• To unikat.
• Jest unikatem.

Both are natural, but the grammar changes.

No. Ten zegar to unikat is a complete and correct sentence.

Polish often uses to instead of jest in present-tense identification sentences, especially when both parts are nouns.

You can also say:

• Ten zegar jest unikatem.

That is also correct, but it is a different structure.

A simple way to think about it:

• X to Y = identification / definition
• X jest Y-em = regular be sentence

In many contexts, both sound natural.

Because unikat is a noun, not an adjective.

It means something like:

• a one-of-a-kind piece
• a rarity
• a unique specimen
• a collector’s item

So Ten zegar to unikat does not literally mean This clock is unique in the adjective sense. It more literally means:

• This clock is a rarity
• This clock is a one-of-a-kind piece

If you wanted an adjective-based sentence, you could say something like:

• Ten zegar jest unikalny.
• Ten zegar jest wyjątkowy.
• To unikatowy zegar.

Those feel a bit different from unikat, which strongly treats the clock as a rare object.

In this sentence:

• ten — nominative singular masculine
• zegar — nominative singular
• to — does not change form here
• unikat — nominative singular

Why nominative for unikat? Because in the X to Y structure, the noun after to is typically nominative.

That is why you get:

• Ten zegar to unikat.

but with jest you often get:

• Ten zegar jest unikatem.

Yes, it is natural, especially if you want to emphasize that the clock is a rare or special object.

It sounds a bit stronger and more specific than simply saying the clock is special. It suggests something more like a rare find, an unusual piece, or an object of value or interest.

So it would fit well in contexts like:

• antiques
• auctions
• museums
• collectors
• descriptions of rare objects

In everyday speech, if you just mean This clock is very special, people might also choose:

• Ten zegar jest wyjątkowy.
• Ten zegar jest naprawdę niezwykły.

But Ten zegar to unikat is absolutely correct and idiomatic.