Neyðarlínan er opin.

• Neyðarlínan = the emergency line
• er = is
• opin = open

Grammatically:

• Neyðarlínan is the subject.
• er is the present-tense form of vera (to be).
• opin is an adjective describing the subject.

So the structure is basically subject + is + adjective, just like in English.

Because Icelandic usually puts the at the end of the noun instead of using a separate word.

The base noun is neyðarlína = emergency line.
When it becomes definite, it becomes neyðarlínan = the emergency line.

This is very common in Icelandic:

• kona = woman
• konan = the woman

So -an here is part of the definite form.

Because many Icelandic compounds use a genitive-style linking form in the first part.

• neyð = emergency / distress
• neyðar- = a compound form meaning something like of emergency

So neyðarlína is literally something like emergency-line or line of emergency.

This pattern is very common in Icelandic compound words.

Because Icelandic adjectives have to agree with the noun in gender, number, and usually case.

neyðarlína is:

• feminine
• singular
• here, nominative

So the adjective must also be feminine singular nominative:

• masculine: opinn
• feminine: opin
• neuter: opið

That is why the sentence has opin.

That is a very good question.

After er (is), the adjective is in predicate position: it tells you what the subject is like. In that position, Icelandic normally uses the strong adjective form.

So:

• Neyðarlínan er opin. = The emergency line is open.

But opna would be the form you expect in certain attributive uses, where the adjective stands directly with the noun inside the noun phrase.

So even though Neyðarlínan is definite, opin is still the correct form here.

Because in this sentence opin is not directly attached to the noun inside a noun phrase. It comes after er and works like English open in The emergency line is open.

So this is a predicate adjective structure:

• Neyðarlínan = the emergency line
• er = is
• opin = open

If you put the adjective directly before the noun, you are making a different kind of structure, more like an open emergency line.

It is in the nominative case, because it is the subject of the sentence.

In a basic statement like this, the subject is normally nominative:

• Neyðarlínan = nominative subject
• er opin = what is being said about the subject

This is one reason the adjective also appears in its nominative feminine singular form.

A rough English-style approximation is:

NAY-thar-LEE-nan er OH-pin

A few helpful details:

• ey sounds roughly like ay in day
• ð sounds like th in this
• í sounds like ee in see
• the stress in Icelandic is usually on the first syllable

So the main stress is on Ney-.

You usually put the verb first:

Er Neyðarlínan opin?
= Is the emergency line open?

This kind of verb-subject inversion is very common in Icelandic yes/no questions.

Here it most naturally means available / operating / open for service.

With things like lines, offices, shops, and services, Icelandic opinn / opin / opið often works like English open in the sense of currently available.

So in this sentence, the idea is not that a literal line is standing open physically, but that the service is open and functioning.