Sykkelsetet er høyt.

Because Norwegian usually writes compound nouns as one word.

• sykkel = bicycle / bike
• sete = seat

So sykkelsete means bicycle seat.

Then -et is added to make it definite:

• et sykkelsete = a bicycle seat
• sykkelsetet = the bicycle seat

This is very normal in Norwegian. Where English often uses two words, Norwegian often makes a compound.

The ending -et is the definite article for many neuter nouns in Norwegian.

The noun is:

• et sete = a seat

When it becomes definite, it changes to:

• setet = the seat

The same happens in the compound:

• et sykkelsete = a bicycle seat
• sykkelsetet = the bicycle seat

So Norwegian often puts the at the end of the noun instead of using a separate word like English does.

Because the adjective has to agree with the noun.

Here, the noun is sykkelsetet, whose head noun is sete.
Sete is a neuter noun:

• et sete

When an adjective comes after er and describes a singular neuter noun, it usually takes -t:

• setet er høyt = the seat is high

Compare:

• en stol er høy = a chair is high/tall
• et bord er høyt = a table is high
• setet er høyt = the seat is high

So høy is the basic form, and høyt is the neuter singular form.

Because høye is used in other situations, not here.

In this sentence, høyt is a predicate adjective: it comes after er and describes the subject.

• Sykkelsetet er høyt. = The bicycle seat is high.

But høye is commonly used:

• with plural nouns
• or in certain definite noun phrases when the adjective comes before the noun

For example:

• høye hus = tall/high houses
• det høye sykkelsetet = the high bicycle seat

So:

• after er with a singular neuter noun: høyt
• before a definite noun: often høye

The dictionary forms are:

• sykkelsete = bicycle seat
• å være = to be
  
  • er = is / are
• høy = high / tall

So the sentence is built from:

• sykkelsete
• er from å være
• høy, which becomes høyt here because of grammar

Because Norwegian often marks definiteness with an ending instead of a separate word.

English:

• the bicycle seat

Norwegian:

• sykkelsetet

The the idea is already included in -et.

However, when you have an adjective before the noun, Norwegian often uses double definiteness:

• det høye sykkelsetet = the high bicycle seat

So in your sentence, no separate the is needed because the noun is definite by itself.

In this sentence, high is usually the better match.

For objects like a seat, table, shelf, or mountain level, Norwegian often uses høy/høyt in a way that corresponds to high in English.

Examples:

• Bordet er høyt. = The table is high.
• Fjellet er høyt. = The mountain is high.

For people, høy often corresponds to tall:

• Han er høy. = He is tall.

So for sykkelsetet, think high, not tall.

It is the normal Norwegian statement order:

subject + verb + complement

• Sykkelsetet = subject
• er = verb
• høyt = adjective complement

So it works very much like English:

• The bicycle seat is high.

This is one of the simpler Norwegian sentence patterns.

A rough guide:

• sykkelsetet ≈ SIK-kel-se-te
• høyt is harder, because of ø and y

A few pronunciation notes:

• y in Norwegian is a rounded vowel that English does not really have.
• ø is also a vowel English lacks.
• In høyt, the vowel sound is a diphthong something like ø+y together.
• The final t is pronounced.

If you want to practice piece by piece:

• sykkel = bike
• sete = seat
• høyt = try starting with a rounded hø sound, then glide toward y, then add t

The hardest parts for English speakers are usually y, ø, and the combination in høyt.

Yes, if the context already makes it clear which seat you mean.

• Setet er høyt. = The seat is high.
• Sykkelsetet er høyt. = The bicycle seat is high.

The longer version is more specific. The shorter version is natural when everyone already knows you are talking about the bike seat.

The indefinite version would be:

Et sykkelsete er høyt.

That means A bicycle seat is high, but in many contexts it sounds more general or less natural unless you really mean a bicycle seat in a non-specific sense.

More commonly, you might say:

• Et sykkelsete kan være høyt. = A bicycle seat can be high.
• Sykkelsetet er høyt. = The bicycle seat is high.

So the sentence you were given is a definite, specific statement.

Not exactly.

• Sykkelsetet er høyt. usually means the seat is set high or is at a high height.
• Sykkelsetet er høyt oppe. means the seat is high up.

The second one focuses more on location or position up high, while the original sentence is the more basic way to say the seat is high.

So they are related, but not identical.