Munnen er tørr.

Because munnen is the definite singular form of munn.

• munn = a mouth
• munnen = the mouth

In Norwegian, definiteness is often shown by adding an ending to the noun:

• en munn = a mouth
• munnen = the mouth

So Munnen er tørr literally has the mouth as its subject.

Er is the present tense of å være, which means to be.

So:

• å være = to be
• er = is / am / are

Examples:

• Munnen er tørr. = The mouth is dry.
• Huset er stort. = The house is big.
• Jeg er trøtt. = I am tired.

Norwegian uses er for all persons in the present tense, unlike English:

• I am
• you are
• he is

but in Norwegian:

• jeg er
• du er
• han er

Because tørr agrees with a singular common-gender noun.

Munn is a common-gender noun (en munn), so the adjective stays in its basic form:

• en tørr munn = a dry mouth
• munnen er tørr = the mouth is dry

Compare that with other forms:

• et tørt brød = a dry bread/piece of bread
• brødet er tørt = the bread is dry
• tørre lepper = dry lips
• leppene er tørre = the lips are dry

So the pattern is:

• common gender singular: tørr
• neuter singular: tørt
• plural: tørre

Not in this sentence.

After er and other forms of to be, the adjective is a predicative adjective, and it agrees mainly with gender and number, not with definiteness in the same way as an adjective before a noun.

So:

• en tørr munn = an indefinite noun, adjective before noun
• munnen er tørr = a definite noun, adjective after er

Even though munnen is definite, the adjective is still tørr because the noun is:

• singular
• common gender

Compare:

• et tørt rom / rommet er tørt
• tørre hender / hendene er tørre

Munn is a common-gender noun.

You can see that from the indefinite article:

• en munn

This matters because gender affects things like:

1. the definite form

   • en munn → munnen

2. adjective agreement

   • en tørr munn
   • munnen er tørr

If it were a neuter noun, the adjective would usually take -t in the singular:

• et tørt ...

So yes, the gender of the noun helps determine the form of the adjective.

A careful approximation is:

• Munnen ≈ MOON-en
• er ≈ air / a short, light er
• tørr ≈ something like turr, but with the Norwegian ø sound

A few pronunciation notes:

• u in munnen is like the vowel in food, but shorter.
• ø in tørr does not exist exactly in English. It is similar to the vowel in French peur or German schön, depending on dialect.
• The rr in tørr may sound different depending on dialect. In some varieties it is a tapped or rolled sound; in others it affects the preceding sound more subtly.

If pronunciation is your focus, tørr is the trickiest word in the sentence.

Yes. This is the normal order for a simple statement:

• Subject + verb + adjective
• Munnen
  • er
    • tørr

This is very similar to English:

• The mouth
  • is
    • dry

Norwegian main clauses usually follow the V2 rule, meaning the finite verb comes in the second position. In a simple sentence like this, that gives the familiar pattern:

• Munnen er tørr.

You would not normally say Tørr er munnen unless you were being poetic or very stylistic.

Grammatically, yes, but it usually would not mean the same thing in normal use.

• En munn er tørr = A mouth is dry
• Munnen er tørr = The mouth is dry

In most everyday situations, en munn er tørr sounds odd unless you are speaking very generally, describing a mouth in a picture, or contrasting it with something else.

If you are talking about a specific person’s mouth, munnen is much more natural.

Yes, it is understandable and correct, but in everyday Norwegian, people often say:

• Jeg er tørr i munnen. = My mouth is dry / I have a dry mouth
• Han er tørr i munnen. = His mouth is dry
• Hun er tørr i munnen. = Her mouth is dry

This structure is very common when talking about how a person feels physically.

So:

• Munnen er tørr. is correct and clear.
• Jeg er tørr i munnen. is often more idiomatic when talking about yourself.

Yes, but it usually sounds more explicit or formal than necessary.

• Min munn er tørr literally means My mouth is dry
• It is grammatically correct

However, in everyday Norwegian, people more often say:

• Jeg er tørr i munnen

Norwegian often prefers a more natural body-part expression rather than explicitly using my with body parts every time.

So Min munn er tørr is possible, but it is less idiomatic in ordinary conversation.

The dictionary forms are:

• munn = mouth
• være = to be
• tørr = dry

In the sentence, they appear as:

• munnen = definite singular of munn
• er = present tense of være
• tørr = adjective in the form that matches a singular common-gender noun

This is useful because when you look words up, you usually need the dictionary form, not the exact form from the sentence.