Pokoj je úplně čistý.

Here pokoj means room.

A useful thing to know is that pokoj can also mean peace in other contexts. Czech learners often notice this double meaning.

Examples:

• Můj pokoj je malý. = My room is small.
• Chci pokoj. = I want peace.

In Pokoj je úplně čistý., the meaning is clearly room because of the adjective čistý (clean).

Because pokoj is the subject of the sentence, it is in the nominative case, which is the basic dictionary form.

So:

• pokoj = nominative singular
• it is the thing being described: The room is ...

Czech changes nouns depending on their role in the sentence, but here no change is needed because the room is the subject.

Je means is. It is the 3rd person singular form of the verb být (to be).

So:

• já jsem = I am
• ty jsi = you are
• on/ona/ono je = he/she/it is

Since pokoj is a singular noun, Czech uses je:

• Pokoj je čistý. = The room is clean.

In the present tense, Czech normally does not leave out the verb to be in sentences like this.

So you say:

• Pokoj je čistý.

Not:

• Pokoj čistý. (not standard as a full neutral sentence)

In some headlines, notes, or very informal elliptical contexts, words may be omitted, but in normal grammar you need je.

Úplně means something like completely, totally, or entirely.

So:

• Pokoj je úplně čistý. = The room is completely/totally clean.

In everyday Czech, úplně is also very common as an intensifier, sometimes closer to really or absolutely, depending on context.

Examples:

• To je úplně jasné. = That is completely clear.
• Jsem úplně unavený. = I’m totally tired.

Because adjectives in Czech must agree with the noun they describe in gender, number, and case.

pokoj is:

• masculine
• singular
• nominative
• specifically masculine inanimate

So the adjective must also be masculine singular nominative:

• čistý

Compare:

• pokoj je čistý = the room is clean
• kuchyň je čistá = the kitchen is clean
• okno je čisté = the window is clean

One clue is its ending: pokoj ends in a consonant, and many Czech nouns ending in a consonant are masculine.

Also, this is something you learn with the noun:

• ten pokoj = that room

Using ten shows it is masculine.

That matters because it affects adjective endings:

• ten čistý pokoj
• pokoj je čistý

Because this sentence uses a predicate adjective, not an adjective directly attached before the noun.

Compare:

1. Čistý pokoj
   = a clean room
   Here the adjective directly modifies the noun.

2. Pokoj je čistý.
   = The room is clean.
   Here the adjective comes after je and describes the subject.

This works much like English:

• a clean room
• the room is clean

It would sound unnatural in a neutral sentence.

The normal position is:

• Pokoj je úplně čistý.

That is because úplně modifies čistý, so it usually comes before it.

Czech word order is flexible, but not random. Changing the position often changes emphasis. A learner should stick with:

• Pokoj je úplně čistý.

Czech has no articles like English a/an/the.

So pokoj can mean:

• a room
• the room

The exact meaning depends on context.

In this sentence, English might translate it as:

• The room is completely clean. or
• A room is completely clean.

But in real usage, the room is much more likely unless the context suggests otherwise.

A simple learner-friendly pronunciation is:

• úplně ≈ OO-pl-nyeh

A few details:

• ú is a long oo
• pl is pronounced clearly; Czech allows consonant clusters
• ně sounds roughly like nye

So the whole word is something like:

• OO-pl-nyeh

A rough English-style guide is:

• čistý ≈ CHIS-tee

More precisely:

• č sounds like ch in chair
• i is a short i
• stý ends with a long ee-like vowel written ý

So:

• čistý ≈ CHIS-tee, with the last vowel held a bit longer.

They are related, but grammatically different.

• čistý pokoj = a clean room
  This is a noun phrase.

• Pokoj je čistý. = The room is clean.
  This is a full sentence.

So if you want to describe a room inside a bigger phrase, use:

• čistý pokoj

If you want to make a complete statement, use:

• Pokoj je čistý.

Yes. That means That room is completely clean or sometimes The room is completely clean, depending on context.

Adding ten makes the noun more specific:

• Pokoj je úplně čistý. = The room is completely clean.
• Ten pokoj je úplně čistý. = That room is completely clean.

Czech often leaves out words like ten unless there is a reason to emphasize or specify.

Because this adjective follows the standard pattern for a hard adjective in the masculine singular nominative.

The basic masculine singular form is:

• čistý

Some adjectives have forms ending in -í, but those belong to different adjective patterns.

For a beginner, the important point is:

• learn the adjective in its dictionary form
• here the dictionary form is čistý
• and it agrees correctly with pokoj

It is a pretty neutral sentence.

• Pokoj = topic / what we are talking about
• je úplně čistý = what we say about it

Because Czech word order is flexible, you could shift things for emphasis, but the given version is natural and straightforward.

For example:

• Pokoj je úplně čistý. = neutral statement
• Úplně čistý je ten pokoj. = marked/emphatic, much less neutral

For normal use, the original sentence is the best choice.