Lestrarsalurinn er opinn.

It is built into lestrarsalurinn.

Icelandic usually puts the definite article on the end of the noun instead of using a separate word like English the. So:

• lestrarsalur = reading room
• lestrarsalurinn = the reading room

So the sentence does not need a separate word for the.

Because Icelandic uses compound nouns very freely.

English often writes this idea as two words, reading room, but Icelandic normally combines the parts into one noun:

• lestur = reading
• salur = hall, room

Together they form lestrarsalur.

This is very common in Icelandic, so long nouns are often easier to understand once you learn to spot the smaller parts inside them.

It comes from lestur and is a compound form meaning something like of reading or for reading.

More specifically, lestrar- is based on the genitive form of lestur. Icelandic often uses this kind of form in compounds. So lestrarsalur is literally something like:

• hall/room for reading
• or reading room

You do not always need to translate the internal grammar literally, but it is helpful to recognize that lestrar- links the idea of reading to the noun that follows.

Er is the present-tense form of vera, the verb to be.

Here it means is:

• Lestrarsalurinn er opinn. = The reading room is open.

It is used with a singular subject here. A useful comparison is:

• er = is
• eru = are

So in the plural you would get eru instead.

Because opinn is a predicate adjective, not an adjective placed directly before the noun.

In this sentence, the structure is:

• Lestrarsalurinn = subject
• er = verb
• opinn = adjective describing the subject after to be

That is the normal pattern for sentences like The reading room is open.

If you put the adjective directly before the noun, that becomes a different structure:

• opinn lestrarsalur = an open reading room
• opni lestrarsalurinn = the open reading room

So after er, the adjective comes later in the sentence.

Because Icelandic adjectives agree with the noun they describe in gender, number, and usually case.

Here, lestrarsalurinn is:

• masculine
• singular
• nominative

So the adjective also appears in the masculine singular nominative form:

• opinn

Compare:

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

So opinn tells you that the noun it refers to is masculine singular here.

That is a very common question.

• opinn is the form used here because the adjective is predicative: it comes after er
• opni is the weak form typically used when the adjective comes directly before a definite noun

Compare:

• Lestrarsalurinn er opinn. = The reading room is open.
• Opni lestrarsalurinn = the open reading room

So the difference is not just vocabulary; it is about the adjective’s grammatical role in the sentence.

Yes.

Lestrarsalurinn is in the nominative singular because it is the subject of the sentence.

With vera (to be), a predicate adjective like opinn is also normally nominative. So both parts line up:

• lestrarsalurinn = nominative singular masculine
• opinn = nominative singular masculine

That agreement is one of the key grammar patterns in Icelandic.

Usually, no. Icelandic does not normally use a separate indefinite article like English a/an.

So:

• lestrarsalur can mean a reading room or just reading room, depending on context
• lestrarsalurinn means the reading room

For example:

• Lestrarsalur er opinn. = A reading room is open / The reading room is open in a more indefinite sense, depending on context
• Lestrarsalurinn er opinn. = The reading room is open

So Icelandic marks definiteness much more clearly than indefiniteness.

You would change both the noun and the verb, and the adjective would also agree.

Singular:

• Lestrarsalurinn er opinn. = The reading room is open.

Plural:

• Lestrarsalirnir eru opnir. = The reading rooms are open.

Changes:

• lestrarsalurinn → lestrarsalirnir
• er → eru
• opinn → opnir

This is a good example of how Icelandic makes agreement visible across the whole sentence.

A rough guide is:

• LES-tra-sah-lu-rinn er OH-pin

A more Icelandic-style approximation in IPA is:

• [ˈlɛstraˌsaːlʏrɪn ɛr ˈɔːpɪn]

A few helpful points:

• Stress usually falls on the first syllable of an Icelandic word.
• The r is pronounced clearly, not swallowed.
• The u in -urinn is not English oo; it is closer to German ü or French u.
• opinn has a short, crisp ending.

You do not need perfect pronunciation immediately, but hearing the stress pattern early is very useful.