Kostnaðurinn er of mikill.

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

So:

• kostnaður = cost
• kostnaðurinn = the cost

That ending changes depending on the noun’s gender, number, and case. Here, -inn is the masculine singular nominative definite ending.

Kostnaður is a masculine noun.

That matters because adjectives in Icelandic must agree with the noun they describe in:

• gender
• number
• case

Since kostnaðurinn is masculine singular nominative, the adjective also appears in the matching form:

• mikill = masculine singular nominative

If the noun were feminine or neuter, the adjective form would change.

Icelandic adjectives change form to match the noun they describe.

The adjective here is mikill, meaning something like big / great / much depending on context. In this sentence, it means too great or too high when talking about cost.

Because kostnaðurinn is:

• masculine
• singular
• nominative

the adjective must be:

• mikill

Other forms include things like:

• mikil for some feminine uses
• mikið for some neuter uses

So mikill is not the dictionary form being used randomly; it is the grammatically correct agreeing form.

Of means too in the sense of excessively.

So:

• of mikill = too great / too much / too high

Be careful not to confuse this with English too meaning also. In Icelandic, those are different words.

Here, of is an adverb modifying the adjective mikill.

This is a very normal Icelandic sentence pattern:

• subject: Kostnaðurinn
• verb: er
• complement: of mikill

So it works like:

• The cost
  • is
    • too high

This is similar to standard English word order in a simple statement.

Er is the present tense singular form of the verb að vera, meaning to be.

In this sentence it means is.

Some common present-tense forms are:

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

So Kostnaðurinn er ... means The cost is ...

Because Icelandic usually expresses the as a suffix on the noun.

So instead of:

• separate the
  • noun

Icelandic often uses:

• noun + definite ending

That is why you get kostnaðurinn rather than a separate article before it.

There are some situations in Icelandic where other determiners appear, but in ordinary definite noun phrases, the suffixed article is the normal pattern.

Yes. Mikill often has a broad meaning such as:

• big
• great
• much

Its most natural English translation depends on context.

With something like cost, English usually prefers:

• high
• great
• too much

So although the adjective is not a one-to-one match with English high, it is completely natural in Icelandic to use mikill with nouns like cost.

Yes, it is nominative here.

You can tell because it is the subject of the sentence:

• Kostnaðurinn = the thing being talked about
• er of mikill = what is being said about it

In dictionary form, the noun is kostnaður. The definite nominative singular form is kostnaðurinn.

The adjective mikill also shows nominative singular masculine agreement, which fits that analysis.

Yes, but the meaning changes slightly.

• Kostnaðurinn er of mikill = The cost is too high
• Kostnaður er of mikill = Cost is too high or The cost is too high in a more general or less specifically marked way, depending on context

In many real situations, the definite form kostnaðurinn sounds more natural when you mean a specific cost already known in the conversation.

A rough guide is:

• KOST-na-thur-inn

A few useful notes:

• ð in Icelandic is like the th in this
• the stress is normally on the first syllable
• au in kostnaður does not sound like English aw in a simple one-to-one way, so it is best learned by listening to native audio

If pronunciation is important for you, it is especially helpful to listen for:

• the first-syllable stress
• the ð sound
• the ending -inn

It is completely normal everyday Icelandic.

It is a straightforward, natural way to say that a cost is excessive. You could use it in many contexts, such as:

• talking about prices
• discussing a project budget
• reacting to a bill
• complaining about fees

So this is a very useful real-life sentence pattern:

• [noun with definite article] + er + of + adjective

Yes. This pattern is very common. For example:

• Verðið er of hátt. = The price is too high.
• Tíminn er of stuttur. = The time is too short.
• Hraðinn er of mikill. = The speed is too great.

These all follow the same structure:

• definite noun
• er
• of
• adjective agreeing with the noun

So Kostnaðurinn er of mikill is a good model sentence to learn from.