Við segjum upp ótímabundnum samningi skriflega.

Because segja upp is a fixed verb expression in Icelandic.

On its own, segja usually means to say / tell. But segja upp has a different meaning, such as:

• to terminate
• to cancel
• to give notice
• in some contexts, to quit or dismiss

So in this sentence, you should learn segja upp as a single lexical unit, not as the ordinary verb segja plus a random extra word.

This is very common in Icelandic with verb-particle combinations.

In a finite clause, the particle often appears after the conjugated verb:

• Við segjum upp samningi.

But in the infinitive, the verb and particle are together:

• að segja upp samningi

So this separation is normal and expected. English does something similar with phrasal verbs:

• We call off the meeting
• to call off the meeting

In Icelandic, segja upp behaves in a comparable way.

Because segja upp takes the dative case for the thing being terminated.

The noun samningur means contract/agreement. Its singular forms include:

• nominative: samningur
• accusative: samning
• dative: samningi
• genitive: samnings

Since segja upp requires the dative, the sentence uses samningi.

This is something learners often just have to memorize with the verb:

• segja upp + dative

Because the adjective must agree with samningi in case, number, and gender.

Here:

• samningi is dative singular
• samningur is masculine
• so the adjective must also be masculine singular dative

That gives:

• ótímabundnum samningi

So the -um ending is there because the whole noun phrase is in the dative singular.

It literally means something like not time-limited or not fixed-term.

You can break it down like this:

• ó- = un- / not
• tímabundinn = temporary / fixed-term / time-limited

So ótímabundinn samningur is an indefinite contract, open-ended contract, or contract without a fixed end date.

In this sentence it appears in the dative form:

• ótímabundnum samningi

Icelandic does not use articles in the same way English does.

There is:

• no separate indefinite article corresponding to English a/an
• a definite article does exist, but it is often attached to the noun as a suffix

So a bare noun phrase like:

• ótímabundnum samningi

can mean:

• an indefinite contract
• the indefinite contract

depending on context.

In many legal or formal sentences, Icelandic often leaves the noun phrase without a definite article where English might choose an or the.

Skriflega means in writing / in written form.

It tells you how the termination is done. So it functions adverbially.

In this sentence, it means that the cancellation or notice must be given in writing, not verbally.

This kind of wording is especially common in formal, legal, or administrative language.

Because here skriflega describes the action of terminating, not the noun samningi.

Compare the difference:

• skriflegur samningur = a written contract
  Here skriflegur is an adjective describing the contract.

• segja upp samningi skriflega = terminate a contract in writing
  Here skriflega describes how the action is carried out.

So in this sentence, skriflega is not modifying samningi. It is modifying the whole verbal idea segjum upp.

Yes, to some extent.

The sentence:

• Við segjum upp ótímabundnum samningi skriflega.

is a normal, natural order.

But Icelandic word order is somewhat flexible, especially with adverbs and heavier noun phrases. For example, you may also see:

• Við segjum skriflega upp ótímabundnum samningi.
• Ótímabundnum samningi segjum við upp skriflega.

These alternatives can sound more marked, formal, or stylistically different depending on context.

The version you were given is straightforward and natural for a neutral statement.

Strictly speaking, the verb ending already shows that the subject is we:

• segjum = we say / we terminate

So Icelandic can sometimes omit subject pronouns.

However, við is still very commonly used for clarity, emphasis, or normal style. In many sentences it sounds perfectly natural to include it.

So:

• Við segjum upp ... = natural
• Segjum upp ... = possible in the right context, but less neutral as a standalone statement

Segjum is the 1st person plural present tense of segja.

So it literally means we say, but with upp it gives the present-tense meaning of we terminate / we give notice / we cancel.

In formal or legal language, the present tense is often used for statements of policy, procedure, or contractual action, much like English does in sentences such as:

• We hereby terminate...
• We give notice...

Yes, it sounds fairly formal and administrative, especially because of:

• segja upp samningi = a legal/contractual expression
• ótímabundnum samningi = technical/formal vocabulary
• skriflega = typical formal wording

This is the kind of sentence you might see in:

• employment documents
• rental agreements
• legal notices
• official instructions

It is not unnatural Icelandic, but it definitely belongs more to formal than casual everyday speech.

A good strategy is to learn it in chunks rather than word by word:

• segja upp + dative = to terminate/cancel
• ótímabundinn samningur = open-ended / indefinite contract
• skriflega = in writing

That way, you remember the important grammar together with the vocabulary:

• the verb requires dative
• the adjective must match the noun
• skriflega is a standard formal adverb

For many learners, the most useful thing to memorize is:

• að segja upp samningi
• að segja upp ótímabundnum samningi skriflega

That helps the case pattern stick much better than memorizing isolated dictionary forms.