Trzeciego grudnia spotkajmy się na rynku o siódmej.

In Polish, a date often appears without any preposition.

So English on the third of December is simply:

trzeciego grudnia

This is the normal way to give a date in a sentence. Polish does not need a separate word equivalent to on here.

For example:

• Przyjadę piątego maja. = I’ll arrive on the fifth of May.
• Spotkajmy się trzeciego grudnia. = Let’s meet on the third of December.

Because in Polish dates use the ordinal number in the genitive case.

The basic form is:

• trzeci = third

But in a date, Polish uses:

• trzeciego = of the third / on the third

This comes from an older full expression that is understood as something like:

• trzeciego dnia grudnia = of the third day of December

Today, dnia is usually omitted, but the genitive form remains.

So:

• trzeciego grudnia = on the third of December

Because the month name also appears in the genitive case in dates.

The dictionary form is:

• grudzień = December

But after the day number in a date, it becomes:

• grudnia

So:

• trzeciego grudnia = the third of December

This happens with all months:

• pierwszego stycznia = the first of January
• piątego maja = the fifth of May
• dwudziestego lipca = the twentieth of July

Spotkajmy się means let’s meet.

It is the 1st person plural imperative, so it includes the speaker and the listener:

• spotkajmy się = let’s meet

The verb is spotkać się = to meet.

The się is part of the verb here. In English we just say meet, but in Polish the natural verb is spotkać się.

Compare:

• Spotkajmy się jutro. = Let’s meet tomorrow.
• Chcę się z tobą spotkać. = I want to meet you.

Because the Polish verb for to meet is usually spotkać się or spotykać się.

This się is very common in Polish and often appears in verbs that are:

• reflexive
• reciprocal
• idiomatic as a fixed expression

Here it is part of the normal way to say meet in the sense of meet each other.

So:

• spotkać by itself can mean to encounter someone
• spotkać się means to meet up / get together

In this sentence, spotkajmy się clearly means let’s meet up.

This is about aspect.

• spotkać się is perfective
• spotykać się is imperfective

In this sentence, the speaker is suggesting one specific meeting at a specific time, so the perfective verb is natural:

• spotkajmy się = let’s meet (once, for that occasion)

If you said:

• spotykajmy się

that would sound more like:

• let’s meet regularly
• let’s keep meeting
• let’s be meeting

So for a one-time planned meeting, spotkajmy się is the right choice.

Because rynek here means market square / town square, and in Polish you normally say:

• na rynku = in the market square / on the square

Polish often uses na with open public spaces, squares, islands, campuses, etc., where English might use in or at.

So:

• na rynku = at the market square
• na placu = in the square
• na ulicy = on the street

For this meaning, na rynku is the standard expression.

Because after na in this meaning, Polish uses the locative case.

The basic form is:

• rynek = market square

After na, it changes to:

• na rynku

This is a normal case change:

• w domu = in the house
• na stole = on the table
• na rynku = at/in the market square

So rynku is simply the locative form of rynek.

When telling the time at a certain hour, Polish uses:

• o + locative

And the hour is often expressed as an ordinal feminine form, because the full idea is:

• o siódmej godzinie = at the seventh hour

Usually godzinie is omitted, leaving:

• o siódmej = at seven

So:

• o pierwszej = at one
• o drugiej = at two
• o siódmej = at seven

You do not normally say o siedem.

No. In normal Polish, godzinie is usually omitted.

So the natural form is:

• o siódmej = at seven

You may sometimes hear or see:

• o siódmej godzinie

but that sounds more formal, old-fashioned, or emphatic in most everyday contexts.

In ordinary speech, just say:

• Spotkajmy się o siódmej.

No, Polish word order is fairly flexible.

This sentence is perfectly natural, but you can move parts around depending on what you want to emphasize.

For example:

• Spotkajmy się trzeciego grudnia na rynku o siódmej.
• Na rynku spotkajmy się trzeciego grudnia o siódmej.
• O siódmej spotkajmy się na rynku trzeciego grudnia.

All of these are possible, though some will sound more natural than others depending on context.

The original version feels like:

• first giving the date
• then the suggestion let’s meet
• then the place
• then the time

Because in Polish, names of months are normally written with a lowercase letter.

So:

• grudzień
• maj
• lipiec

This is different from English, where December and May are capitalized.

So the correct Polish spelling is:

• trzeciego grudnia not
• trzeciego Grudnia

Yes. In writing, Polish often uses a numeral:

• 3 grudnia

But when read aloud, it is usually read as:

• trzeciego grudnia

So these are equivalent in meaning:

• Spotkajmy się 3 grudnia.
• Spotkajmy się trzeciego grudnia.

The first is more common in practical writing, while the second shows the full spoken form.