Sommerdekket har et godt dekkmønster.

Because sommerdekket is the definite singular form of a neuter noun.

The base noun is sommerdekk = summer tire / summer tyre.
Since dekk is a neuter noun, its definite singular form takes -et:

• et sommerdekk = a summer tire
• sommerdekket = the summer tire

So -et here means the.

Because dekkmønster is also a neuter noun.

In Norwegian, adjectives change form depending on the gender of the noun. With an indefinite singular neuter noun, the adjective usually gets -t.

So:

• et dekkmønster = a tread pattern
• et godt dekkmønster = a good tread pattern

Compare:

• en god bil = a good car
• et godt dekkmønster = a good tread pattern

So godt is used because dekkmønster is neuter.

Dekkmønster is a compound noun:

• dekk = tire / tyre
• mønster = pattern

Together, dekkmønster means tire tread pattern or simply tread pattern.

This is very common in Norwegian: two nouns are joined to make one more specific noun.

Yes. It is made from:

• sommer = summer
• dekk = tire / tyre

So:

• et sommerdekk = a summer tire
• sommerdekket = the summer tire

Norwegian uses compound nouns very often, much like German. English sometimes writes similar ideas as separate words, but Norwegian often writes them as one word.

Because Norwegian often adds definiteness to the end of the noun instead of using a separate article like English the.

So instead of saying something like the summer tire with a separate word for the, Norwegian usually says:

• sommerdekket

This is normal for many nouns:

• en bil = a car
• bilen = the car
• et hus = a house
• huset = the house

So the the meaning is built into the noun.

Because the sentence contains two different noun phrases:

1. Sommerdekket = the summer tire
   This is a definite noun, and the definiteness is already shown by -et.

2. et godt dekkmønster = a good tread pattern
   This is an indefinite noun phrase, so it uses the article et.

So the sentence structure is:

• Sommerdekket = subject
• har = has
• et godt dekkmønster = object

Har is the present tense of å ha, which means to have.

So:

• å ha = to have
• har = have / has

In this sentence, Sommerdekket har ... means The summer tire has ...

This is the normal Norwegian word order for a basic statement:

Subject + verb + object

So here:

• Sommerdekket = subject
• har = verb
• et godt dekkmønster = object

This works very much like English:

• The summer tire
  • has
    • a good tread pattern

Because god is an adjective, and adjectives change form to match the noun.
But sommer is part of a compound noun, not an adjective in this sentence.

So:

• god is an adjective, so it changes:
  • en god bil
  • et godt dekkmønster

But in sommerdekk, sommer is just the first part of a compound noun. It stays as it is.

You can think of sommerdekk as a single vocabulary item meaning summer tire, not as summer behaving like a regular adjective.

Yes, it is the same noun dekk, meaning tire / tyre.

It appears in two different compounds:

• sommerdekk = summer tire
• dekkmønster = tire tread pattern

This repetition is very natural in Norwegian. A single noun often appears inside several compound words.

It would be:

Et sommerdekk har et godt dekkmønster.

That means A summer tire has a good tread pattern.

Compare:

• Et sommerdekk = a summer tire
• Sommerdekket = the summer tire

So the sentence you were given is definite in the subject, but the object remains indefinite.

In normal speech, the d in godt is often not pronounced clearly. It is commonly pronounced roughly like gott.

So although it is written godt, the spoken form is often closer to:

• gott

This is a common feature in Norwegian pronunciation. The spelling keeps the historical d, but speech often simplifies it.

Here are the common forms:

For dekk:

• et dekk = a tire
• dekket = the tire
• dekk = tires
• dekkene = the tires

For sommerdekk:

• et sommerdekk = a summer tire
• sommerdekket = the summer tire
• sommerdekk = summer tires
• sommerdekkene = the summer tires

For dekkmønster:

• et dekkmønster = a tread pattern
• dekkmønsteret = the tread pattern
• dekkmønstre = tread patterns
• dekkmønstrene = the tread patterns

Many neuter nouns have no ending in the indefinite plural, though not all behave exactly the same way.