Kaffibollinn er of heitur.

Because Icelandic very often makes compound nouns as a single word.

• kaffi = coffee
• bolli = cup

So kaffibolli literally means coffee-cup, i.e. coffee cup.

A useful rule: in Icelandic compounds, the last part usually determines the grammatical gender and basic behavior of the whole word. Since bolli is masculine, kaffibolli is masculine too.

The ending -inn is the definite article attached to the noun.

• kaffibolli = a coffee cup
• kaffibollinn = the coffee cup

Unlike English, Icelandic often puts the onto the end of the noun instead of using a separate word.

Here, -inn is the masculine singular nominative definite ending.

It is singular nominative.

Why nominative? Because it is the subject of the sentence:

• Kaffibollinn = the subject
• er = is
• of heitur = too hot

So the sentence structure is basically The coffee cup is too hot.

The dictionary form is kaffibolli, which is the indefinite nominative singular form.

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

Here, kaffibollinn is:

• masculine
• singular
• nominative

So the adjective has to match that, giving heitur.

Compare:

• masculine: heitur
• feminine: heit
• neuter: heitt

So if the noun were neuter, you would get heitt instead.

No. In this sentence, of means too in the sense of excessively.

So:

• of heitur = too hot

It is not related to the English preposition of.

A useful comparison:

• heitur = hot
• mjög heitur = very hot
• of heitur = too hot
• alltof heitur = much too hot / far too hot

So of suggests that the heat is a problem or more than desired.

Yes. This is a normal, neutral Icelandic statement:

• Kaffibollinn = subject
• er = verb
• of heitur = complement

So the pattern is basically subject + verb + complement.

Also, Icelandic is a verb-second language in main clauses, which means the finite verb often comes in the second position. In this simple sentence, that gives the same order you might expect from English.

Yes, it would.

In Kaffibollinn er of heitur, the adjective is predicative: it comes after er and describes the subject. That is why you get heitur.

If the adjective comes directly before the noun, it is attributive, and with a definite noun it usually takes a weak form:

• heitur kaffibolli = a hot coffee cup
• heiti kaffibollinn = the hot coffee cup

So yes, the form changes depending on how the adjective is used.

A rough learner-friendly approximation is:

KAH-fi-boht-linn er of HAY-tur

A few pronunciation notes:

• Stress is on the first syllable of each word.
• In kaffibollinn, the ll is not pronounced like a normal English double l. In this kind of word, Icelandic ll often sounds more like a tl-type sound.
• heitur begins with hei-, which sounds like hay.

So kaffibollinn can sound surprisingly unlike its spelling to English speakers.

It refers to the coffee cup.

That is because kaffibolli means coffee cup. If you wanted to say the coffee is too hot, you would say:

• Kaffið er of heitt.

So the noun matters a lot here:

• kaffibollinn = the coffee cup
• kaffið = the coffee

That distinction is easy for English speakers to miss at first.