Kompromisset er rimelig.

Because kompromisset is the definite singular form of the noun.

• et kompromiss = a compromise
• kompromisset = the compromise

This follows a very common Norwegian pattern for neuter nouns:

• et hus → huset
• et eple → eplet
• et kompromiss → kompromisset

So the ending -et here means the.

You know it from the article in its basic form: et kompromiss.

In Norwegian, nouns are usually learned with their article:

• en = common gender
• et = neuter

Since it is et kompromiss, it is a neuter noun. That is why the definite form is kompromisset.

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

So:

• jeg er = I am
• du er = you are
• det er = it is
• kompromisset er rimelig = the compromise is reasonable/fair

This sentence is simply using the normal present tense.

Here, rimelig is an adjective.

It describes kompromisset, but it comes after the verb er, so it is being used as a predicate adjective.

Compare:

• et rimelig kompromiss = an adjective placed before the noun
• kompromisset er rimelig = an adjective placed after er

Both are normal in Norwegian.

That is a very common learner question.

Normally, predicate adjectives in Norwegian often agree with the noun:

• Bilen er stor = the car is big
• Huset er stort = the house is big

But many adjectives ending in -ig do not usually add -t in neuter singular in everyday Bokmål.

So you commonly get:

• Det er viktig
• Huset er viktig for dem
• Kompromisset er rimelig

With rimelig, the form rimelig is the standard and natural one here.

It can mean several related things, depending on context.

Common meanings include:

• reasonable
• fair
• modest
• inexpensive / affordable

So rimelig is a useful word, but its exact meaning depends on what is being described.

Examples:

• Det er en rimelig pris = that is a reasonable / affordable price
• Det virker rimelig = that seems reasonable
• Et rimelig krav = a fair or reasonable demand

In Kompromisset er rimelig, the sense is most likely reasonable or fair.

No, this sentence has very straightforward word order.

It follows this pattern:

• subject
  • verb
    • adjective/complement

So:

• Kompromisset = subject
• er = verb
• rimelig = complement

This is very similar to English:

• The compromise is reasonable

Yes, but it means something slightly different.

• Et kompromiss er rimelig = A compromise is reasonable
• Kompromisset er rimelig = The compromise is reasonable

The first is more general or indefinite. The second refers to a specific compromise already known in the conversation.

A simple learner-friendly approximation would be:

• kom-pro-MISS-et er RIM-e-li

A few helpful notes:

• kompromisset has the stress on miss
• rimelig usually has the stress on the first syllable: RIM
• the r sound is Norwegian, so it may sound different from many English accents
• the final g in rimelig is often weak or softened in normal speech

You do not need perfect pronunciation at first; getting the stress in the right place helps a lot.

Because Norwegian, like English, does not need an extra dummy subject here when the real subject is already present.

The subject is already Kompromisset.

So the structure is simply:

• Kompromisset = the compromise
• er = is
• rimelig = reasonable

You only use det when det itself is the subject, for example:

• Det er rimelig = it is reasonable

But in your sentence, kompromisset is the subject, so det is not needed.