Það er einn möguleiki.

In this sentence, það is often functioning like a dummy subject: a grammatical placeholder.

So although það usually means it/that, in sentences like Það er ..., it can work a lot like English there is ... or it is ..., depending on context.

So:

• Það er einn möguleiki.
  can be understood structurally as There is one possibility.

This is very common in Icelandic.

Er is the present tense, 3rd person singular form of the verb vera (to be).

So:

• vera = to be
• er = is

Because það is grammatically singular, the verb is singular too:

• Það er ... = There is ... / It is ...

Because einn has to agree with the noun möguleiki in gender, number, and case.

The noun möguleiki (possibility/option) is:

• masculine
• singular
• here in the nominative

So the correct form is:

• masculine nominative singular: einn

Compare:

• einn = masculine
• ein = feminine
• eitt = neuter

So einn möguleiki is correct because möguleiki is a masculine noun.

It can do both, depending on context.

In Icelandic, there is no separate indefinite article like English a/an. So Icelandic often just uses the noun by itself, or sometimes uses einn when the speaker wants to emphasize one or introduce something as a certain one.

So:

• möguleiki = a possibility / possibility
• einn möguleiki = one possibility or sometimes a possibility, with a bit more emphasis

In many contexts, einn sounds more specific or more clearly numerical than English a.

Yes, absolutely.

That often sounds more natural if you simply mean:

• There is a possibility.

Meanwhile:

• Það er einn möguleiki.

more strongly suggests:

• There is one possibility
• or There is a certain possibility/option

So the difference is roughly:

• Það er möguleiki. = a possibility exists
• Það er einn möguleiki. = there is one possibility / one option

It is in the nominative singular.

You can tell because:

• the dictionary form is möguleiki
• einn is also in the masculine nominative singular

After vera (to be), predicate nouns are often in the nominative. In a sentence like this, einn möguleiki is the noun phrase linked by er.

Because Icelandic works differently from English.

English has:

• a possibility
• the possibility

Icelandic does not have a separate word for a/an. Instead:

• an indefinite noun is often just the bare noun
• definiteness is usually shown with a suffixed article

So:

• möguleiki = a possibility / possibility
• möguleikinn = the possibility

That final -inn is the definite article attached to the noun.

A rough guide:

• þ is like English th in thing
• ð is like English th in this, though in Icelandic it can be weaker depending on position
• ei in einn sounds roughly like ay in day, though Icelandic pronunciation is not exactly the same as English

Very roughly, the whole sentence sounds something like:

• THA-th er aytn MÖ-gu-li-ki

But that is only approximate. A few important points:

• það is usually pronounced something like thath
• er is short, like ehr
• einn may sound closer to eintn or ein-n, depending on carefulness and dialect
• stress in Icelandic usually falls on the first syllable of a word:
  • MÖ-gu-lei-ki

Because this is a normal declarative sentence with the subject first and the verb second.

Icelandic is a verb-second language in many contexts, which means the finite verb often comes in the second position. Here that pattern is satisfied:

1. Það
2. er
3. einn möguleiki

So the order is perfectly normal.

You can change word order in some cases for emphasis or in questions, but Það er einn möguleiki is the standard neutral order.

You usually make it a yes/no question by putting the verb first:

• Er það einn möguleiki?

That means:

• Is that one possibility?
• or, depending on context, Is there one possibility?

Icelandic often forms yes/no questions this way: verb + subject.

You add ekki (not) after the verb:

• Það er ekki einn möguleiki.

But be careful: that specifically means something like:

• It is not one possibility
• or There isn’t just one possibility

If you want to say There is no possibility, a more natural sentence would often be:

• Það er enginn möguleiki.

Here enginn means no / not any, and it also agrees with the masculine noun möguleiki.

If you want to talk about more than one possibility, both the verb and the noun phrase change:

• Það eru möguleikar. = There are possibilities.
• Það eru tveir möguleikar. = There are two possibilities.

Notice the changes:

• er → eru because the complement is plural
• möguleiki → möguleikar in the plural
• tveir is the masculine plural form of two

The dictionary form is:

• möguleiki = possibility, option

It is a masculine noun, and its nominative singular ends in -i, which is a common masculine pattern in Icelandic.

A learner will often need to memorize for each noun:

• gender
• singular forms
• plural forms
• any irregularities

For this sentence, the key thing is simply that möguleiki is masculine, which is why you get einn möguleiki.

It can be either, depending on context.

Möguleiki can mean:

• possibility
• option
• chance in some contexts

So Það er einn möguleiki could mean:

• There is one possibility
• There is one option

The surrounding conversation would decide which English translation fits best.