Þær byrjuðu að rífast í eldhúsinu, og rifrildið stóð lengur en ég bjóst við.

Þær means they, specifically for an all-feminine group.

Icelandic has grammatical gender, and the 3rd person plural pronoun changes depending on the gender of the people or things being referred to:

• þeir = they for a masculine or mixed-gender group
• þær = they for a feminine group
• þau = they for a neuter group, or sometimes for mixed things/non-human referents

So in this sentence, þær byrjuðu... tells you that the people involved are feminine.

Byrjuðu is the past tense, plural form of byrja, meaning to begin/start.

The subject is þær = they, so the verb must also be plural.

A quick comparison:

• ég byrjaði = I started
• þú byrjaðir = you started
• hún byrjaði = she started
• við byrjuðum = we started
• þið byrjuðuð = you all started
• þær byrjuðu = they started

So þær byrjuðu = they started.

After byrja in Icelandic, you very often use að + infinitive, just like to + verb in English.

So:

• byrja að lesa = start to read
• byrja að tala = start to speak
• byrja að rífast = start arguing / start to argue

Here, að rífast is the infinitive phrase that tells us what they started doing.

Rífast means to argue, quarrel, bicker.

It usually describes a disagreement between people, often a verbal one. It is not necessarily as strong as physical fighting; it is more like arguing with each other.

So:

• Þær byrjuðu að rífast = They started arguing

This verb often implies mutual action, so English argue with each other is a good way to think about it.

The -st ending is very common in Icelandic and often marks what is traditionally called the middle voice.

In practice, verbs ending in -st can have meanings like:

• reciprocal action: doing something to each other
• reflexive-like meaning
• a special idiomatic meaning that just has to be learned as part of the verb

With rífast, the -st form is the normal verb for argue/quarrel. So it is best to learn rífast as a whole vocabulary item.

You do not need to translate the -st separately every time, but it helps to know that it often gives a sense like engaging in an action mutually.

Í eldhúsinu means in the kitchen, with the definite article built into the noun.

Breakdown:

• eldhús = kitchen
• eldhúsi = kitchen in dative singular
• eldhúsinu = in the kitchen / the kitchen in dative singular definite

Icelandic usually adds the as a suffix rather than as a separate word.

So:

• í eldhúsi = in a kitchen
• í eldhúsinu = in the kitchen

Because í can take either the accusative or the dative, depending on meaning:

• accusative = motion into something
• dative = location in something

Compare:

• ég fer í eldhúsið = I go into the kitchen
  motion → accusative
• ég er í eldhúsinu = I am in the kitchen
  location → dative

In your sentence, the arguing happens in the kitchen, so this is location, not movement. That is why Icelandic uses the dative: í eldhúsinu.

Rifrildið means the argument or the quarrel.

It is a noun, while rífast is the verb.

So the sentence moves from the action to the event as a thing:

• þær byrjuðu að rífast = they started arguing
• rifrildið stóð... = the argument lasted...

This kind of shift is very natural in Icelandic and English alike.

The ending -ið is the definite article attached to the noun.

So:

• rifrildi = an argument / a quarrel
• rifrildið = the argument / the quarrel

This noun is neuter, and in the nominative/accusative singular definite form it becomes rifrildið.

Icelandic usually expresses the by attaching it to the noun itself.

Yes, stóð is the past tense of standa, which literally means stand. But Icelandic often uses standa in a broader sense, including continue, last, or go on.

So:

• rifrildið stóð lengur... = the argument lasted longer...

This is a very natural Icelandic way to express duration. English also sometimes does something similar in older or more formal phrasing, but lasted is the most natural translation here.

This means longer than I expected.

Breakdown:

• lengur = longer
• en = than
• ég bjóst við = I expected

So literally:

• the argument stood longer than I expected

More natural English:

• the argument lasted longer than I expected

This comes from the verb búast við, which means to expect.

It is another -st verb, and it is normally used with við.

Present tense:

• ég býst við = I expect

Past tense:

• ég bjóst við = I expected

So in the sentence:

• en ég bjóst við = than I expected

The thing expected is understood from context, so Icelandic does not need to repeat it.

No, nothing is missing. Icelandic often leaves the expected thing unstated when it is obvious from context.

Here, the comparison is about duration:

• rifrildið stóð lengur en ég bjóst við
• literally: the argument lasted longer than I expected

English does the same thing. You could expand it if you wanted:

• ...lengur en ég bjóst við að það myndi standa
• ...longer than I expected it would last

But the shorter version is much more natural.

En means than in comparisons.

Examples:

• stærri en = bigger than
• betri en = better than
• lengur en = longer than

So:

• lengur en ég bjóst við = longer than I expected

Do not confuse this with other Icelandic words that can mean and or but in different contexts. In this sentence, en is simply the comparison word than.

The sentence has two main parts joined by og = and:

1. Þær byrjuðu að rífast í eldhúsinu
   = They started arguing in the kitchen

2. og rifrildið stóð lengur en ég bjóst við
   = and the argument lasted longer than I expected

So the full structure is:

• subject + past verb + infinitive phrase + location
• and
• subject + past verb + comparative phrase

It is a very natural Icelandic sentence with ordinary word order.

Yes, depending on context, that can be a very natural English translation.

More literal:

• they started arguing

More idiomatic in some situations:

• they got into an argument
• they began to quarrel

The Icelandic focuses on the start of the arguing itself, so started arguing is the closest direct match. But got into an argument can sound very natural in English.

A useful mini-list would be:

• þær = they, feminine plural
• byrja = begin, start
• að = to, before an infinitive
• rífast = argue, quarrel
• í = in, into
• eldhús = kitchen
• rifrildi = argument, quarrel
• standa = stand; also last, continue
• lengur = longer
• en = than
• búast við = expect

This sentence is especially good for practicing:

• gendered pronouns
• að + infinitive
• dative after í for location
• the suffixed definite article
• the expression búast við