Samtengingin er stutt, en mjög mikilvæg.

Samtengingin = samtenging + the suffixed definite article -in.

• samtenging = conjunction
• -in = the

So Samtengingin means the conjunction.

It is:

• singular
• feminine
• nominative (the subject form)

In Icelandic, the definite article is very often added to the end of the noun instead of appearing as a separate word.

So:

• samtenging = conjunction
• samtengingin = the conjunction

This is one of the big differences from English. Icelandic does have separate article-like forms such as hinn / hin / hið, but in ordinary sentences the suffixed article is much more common.

Er is the present tense singular form of vera, which means to be.

So:

• ég er = I am
• þú ert = you are
• hann / hún / það er = he / she / it is

In this sentence, Samtengingin is singular, so er means is.

Because the adjective has to match the noun it describes.

Here, Samtengingin is:

• feminine
• singular
• nominative

The adjective stuttur (short) changes form depending on gender, number, and case. Its nominative singular forms are:

• masculine: stuttur
• feminine: stutt
• neuter: stutt

Since samtenging is feminine singular, the correct form is stutt.

For the same reason: adjective agreement.

The base adjective is mikilvægur (important), but its form changes. In nominative singular:

• masculine: mikilvægur
• feminine: mikilvæg
• neuter: mikilvægt

Because samtengingin is feminine singular, the correct form here is mikilvæg.

Because Icelandic adjectives do not all decline in exactly the same way.

Even though both adjectives are feminine singular nominative here, they belong to different adjective patterns:

• stuttur → feminine stutt
• mikilvægur → feminine mikilvæg

So the important thing is not that all feminine adjectives end the same way, but that each adjective follows its own declension pattern.

Mjög means very.

So:

• mikilvæg = important
• mjög mikilvæg = very important

Mjög is an adverb, so it does not change form to match gender, number, or case. It stays mjög.

Here, en means but.

So the structure is:

• Samtengingin er stutt = The conjunction is short
• en mjög mikilvæg = but very important

A useful extra note: en can also mean than in comparative sentences, but in this sentence it clearly means but.

The comma separates the two coordinated parts of the sentence:

• Samtengingin er stutt
• en mjög mikilvæg

A comma before en is normal in Icelandic writing in this kind of sentence. This may feel a little different from English punctuation habits, which are sometimes less consistent in short sentences like this.

Because Icelandic, like English, can leave out a repeated verb when the structure is clear.

The full idea is:

• Samtengingin er stutt, en (er) mjög mikilvæg.

But repeating er is unnecessary, so it is omitted.

English does the same thing:

• The conjunction is short, but very important.

We understand that is applies to both adjectives.

They are predicate adjectives, which means they come after er and describe the subject through the verb to be.

So this is not like:

• stutta samtengingin = the short conjunction

Instead, it is:

• Samtengingin er stutt = The conjunction is short

That is why the adjectives appear after er.

Yes. Samtengingin is the subject.

You can tell because:

• it is in the nominative
• it is what the sentence is talking about
• the verb er agrees with it as a singular subject

The rest of the sentence says two things about that subject:

• it is stutt
• it is mjög mikilvæg

Yes. That is a very natural English translation.

Even though the meaning has already been given, it is helpful to notice that Icelandic and English behave similarly here: one is/er can cover both adjectives.

So the smooth English structure is:

• The conjunction is short, but very important.

That matches the Icelandic structure closely.