Reservnyckeln tillhör bilhandlaren.

Because Swedish very often makes compound nouns by writing them as a single word.

• reserv = spare / reserve
• nyckel = key

So:

• reservnyckel = spare key

This is much more natural in Swedish than writing separate words. English often uses two words where Swedish prefers one compound word.

The -n marks the noun as definite singular: the spare key.

Compare:

• en reservnyckel = a spare key
• reservnyckeln = the spare key

In Swedish, the definite article is usually attached to the end of the noun instead of being a separate word like the in English.

Here the base word is reservnyckel, and the definite form becomes reservnyckeln.

For the same basic reason: it is also definite singular.

• en bilhandlare = a car dealer
• bilhandlaren = the car dealer

So the sentence uses two definite nouns:

• reservnyckeln = the spare key
• bilhandlaren = the car dealer

This is completely normal in Swedish.

tillhör means belongs to.

It is the present tense of the verb tillhöra.

• att tillhöra = to belong to
• tillhör = belongs to / belong to

So:

• Reservnyckeln tillhör bilhandlaren. = The spare key belongs to the car dealer.

It is a fairly neutral, standard verb for ownership or association.

Because Swedish uses the single verb tillhöra, which already includes the idea of belong to.

English splits it up:

• belongs + to

Swedish keeps it in one verb:

• tillhör

So you say:

• Nyckeln tillhör mannen. = The key belongs to the man.

not something like tillhör till.

It is the thing or person that the spare key belongs to.

In grammar terms:

• Reservnyckeln = subject
• tillhör = verb
• bilhandlaren = object/complement after the verb

So the structure is:

[The spare key] [belongs to] [the car dealer].

Even though English uses to, Swedish does not need a preposition here.

More or less, yes.

It is made up of:

• bil = car
• handlare = dealer / trader / seller

So bilhandlare means car dealer.

Depending on context, it can refer to:

• the dealer as a business
• a person working as a dealer
• a salesman at a dealership

In this sentence, car dealer is the most natural translation.

Because this is a normal main clause in Swedish with standard word order:

subject + verb + object/complement

So:

• Reservnyckeln = subject
• tillhör = verb
• bilhandlaren = object/complement

This is the same basic order as in English:

• The spare key belongs to the car dealer.

Swedish main clauses usually follow the V2 rule (the finite verb comes in the second position), and this sentence fits that pattern perfectly.

Yes, that is possible, but it is a slightly different structure.

• Reservnyckeln tillhör bilhandlaren. = The spare key belongs to the car dealer.

• Reservnyckeln är bilhandlarens. = The spare key is the car dealer’s.

Both are correct. The first uses the verb tillhöra. The second uses a possessive form (bilhandlarens).

The version with tillhör often sounds a bit more straightforward for stating ownership.

Because Swedish usually puts the definite article at the end of the noun as a suffix.

So instead of:

• the spare key
• the car dealer

Swedish says:

• reservnyckeln
• bilhandlaren

This is one of the biggest differences from English.

A very rough pattern is:

• en word → definite form often ends in -en or -n
• ett word → definite form often ends in -et or -t

Both nouns in your sentence are en-words.

You usually learn the definite form together with the noun.

For these words:

• en nyckel → nyckeln
• en reservnyckel → reservnyckeln
• en bilhandlare → bilhandlaren

Many common-gender nouns take -en, but some nouns—especially certain ones ending in unstressed -el, -er, or -en—can show slightly different patterns, such as just -n after a small stem change.

So it is best to learn nouns like this:

• en nyckel, nyckeln
• en bilhandlare, bilhandlaren

not just the indefinite form by itself.

No. It can also mean belong to in a broader sense, such as being part of a group, category, or organization.

For example:

• Hon tillhör styrelsen. = She belongs to the board / is part of the board.

• Det här tillhör en annan kategori. = This belongs to another category.

So in your sentence it expresses ownership, but the verb is not limited to that meaning.

A simple learner-friendly guide would be:

Reservnyckeln tillhör bilhandlaren

Approximate pronunciation: reh-SAIRV-nyck-eln til-HUR beel-hand-lar-en

A few notes:

• y in Swedish is not like English y. It is a rounded vowel that many learners need to practice.
• ö in tillhör is also a special Swedish vowel.
• The stress is usually on the main part of each word:
  • reservnyckeln
  • tillhör
  • bilhandlaren

A perfect accent is not necessary at first, but the vowels matter a lot in Swedish.

Sometimes, yes. Depending on context, you might also hear:

• extranyckel = extra key

But reservnyckel is a very natural word for spare key. It suggests a backup key kept in reserve.

So:

• Reservnyckeln tillhör bilhandlaren.

is a completely normal sentence.

If you wanted an indefinite version, you could say:

• En reservnyckel tillhör en bilhandlare.

That means:

• A spare key belongs to a car dealer.

Grammatically correct, yes—but less natural unless you are speaking very generally. The original definite sentence is more likely in a real situation, because it refers to a specific spare key and a specific car dealer.