Den tamme katten vi adopterte sover i buret.

Because Norwegian usually uses double definiteness when a noun is:

• definite and
• has an adjective in front of it.

So you get:

• katten = the cat
• den tamme katten = the tame cat

Here, den goes with the adjective phrase, and katten is also in the definite form. This is very normal in Bokmål.

The adjective changes form because it is part of a definite noun phrase.

Compare:

• en tam katt = a tame cat
• den tamme katten = the tame cat

In definite phrases with den/det/de, adjectives usually take the -e form:

• den store bilen = the big car
• det store huset = the big house
• de store bilene = the big cars

So tamme is the correct form here.

Because katten is the definite form of katt.

• en katt = a cat
• katten = the cat

Since the sentence refers to a specific cat, Norwegian uses the definite form katten. And because there is also an adjective, you get the full pattern:

• den tamme katten

In Norwegian, the relative word som is often left out when it would be the object of the clause.

So:

• katten vi adopterte = the cat (that) we adopted
• katten som vi adopterte = also possible

Both are grammatical, but leaving out som is very common here.

A useful contrast:

• katten som sover = the cat that is sleeping

Here som is needed because the cat is the subject of the relative clause.

Adopterte is the past tense (preterite) of å adoptere.

• adopterer = adopt / am adopting
• adopterte = adopted

So vi adopterte means we adopted.

The sentence has:

• a past action in the relative clause: we adopted
• a present action in the main clause: sleeps

That combination is completely normal: the adoption happened earlier, and now the cat is sleeping.

Because Norwegian main clauses normally follow the V2 rule: the finite verb comes in the second position.

In this sentence, the whole subject phrase counts as the first unit:

• Den tamme katten vi adopterte = first element
• sover = second element

So the structure is:

• [Den tamme katten vi adopterte] [sover] [i buret]

Even though the subject is long, it still counts as one chunk before the verb.

I buret means in the cage, while i et bur means in a cage.

So the choice depends on whether the cage is:

• specific/known → i buret
• non-specific → i et bur

The sentence uses buret, the definite form, so it refers to a particular cage.

Bur is a neuter noun in Bokmål:

• et bur = a cage
• buret = the cage

That is why the definite ending is -et.

Compare:

• en bil → bilen
• et hus → huset
• et bur → buret

So i buret is exactly what you would expect from a neuter noun.

Yes. That is also correct.

• Den tamme katten vi adopterte sover i buret
• Den tamme katten som vi adopterte sover i buret

Both mean the same thing. The version without som is often a little more natural in everyday Norwegian when the relative word would be the object, as it is here.

So a learner should recognize both patterns.