Ég mæli hitann aftur, því hitamælirinn sýndi ekki mikinn hita.

Because Icelandic usually uses the simple present where English often uses either simple present or present progressive.

So Ég mæli hitann aftur can mean:

• I measure the temperature again
• I’m measuring the temperature again
• in some contexts even I’ll measure the temperature again

The exact meaning comes from context, not from a special progressive form. Icelandic does not have a normal everyday verb form that works exactly like English am measuring.

That is a very common point of confusion.

The verb mæla can mean different things depending on how it is used:

• mæla eitthvað = measure something
• mæla með einhverju = recommend something, literally speak in favor of

In your sentence, mæli hitann has a direct object, hitann, so it clearly means measure the temperature.

So:

• Ég mæli hitann = I measure the temperature
• Ég mæli með þessu = I recommend this

Because hitann is the accusative definite singular form of hiti.

The dictionary form is:

• hiti = heat, temperature, fever

But here it is the direct object of mæli, so Icelandic uses the accusative case. Also, the sentence is talking about the temperature, not just temperature in general, so it takes the suffixed definite article -nn.

A useful mini-chart:

• hiti = nominative singular, indefinite
• hitinn = nominative singular, definite
• hita = accusative singular, indefinite
• hitann = accusative singular, definite

So Ég mæli hitann literally means I measure the temperature.

For the same basic reason: it is a definite singular noun, here in the nominative, because it is the subject of sýndi.

The base noun is:

• hitamælir = thermometer

With the suffixed definite article:

• hitamælirinn = the thermometer

So:

• hitamælirinn sýndi = the thermometer showed

Icelandic usually adds the to the end of the noun instead of putting a separate word before it.

Because mikinn has to agree with hita in gender, number, and case.

The noun hiti is masculine singular. In this sentence it is the direct object of sýndi, so it is in the accusative singular: hita.

The adjective mikill must match that form, so it becomes:

• mikinn hita = much heat / a high temperature / much fever

Why not mikið?

• mikið is neuter
• hiti is masculine

Why not hiti?

• because after sýndi, the object is accusative, so you need hita

So the phrase is grammatically:

• adjective: mikinn
• noun: hita

Both are masculine accusative singular.

Because Icelandic normally keeps the object in its usual case here, even under negation.

The verb sýna takes a direct object in the accusative, so:

• sýndi mikinn hita = showed a high temperature
• sýndi ekki mikinn hita = did not show a high temperature

The ekki simply negates the verb phrase. It does not force the noun into some different case.

Also, mikinn hita sounds more natural here than a very literal English-style much heat. In context, it means something like:

• a high temperature
• much of a fever
• much heat

Here því means because or for.

So the sentence structure is:

• Ég mæli hitann aftur = main clause
• því hitamælirinn sýndi ekki mikinn hita = reason

In natural English, this is:

• I’m checking the temperature again, because the thermometer didn’t show much of a temperature or more idiomatically:
• I’m checking the temperature again, because the thermometer didn’t show much of a fever
• ...because the thermometer didn’t show a high reading

A learner should know that því can have other meanings in other contexts, but in this sentence it is functioning as a conjunction meaning because.

Yes. Af því að is another very common way to say because.

So you could say:

• Ég mæli hitann aftur, af því að hitamælirinn sýndi ekki mikinn hita.

That would sound very natural too.

Very roughly:

• því can feel a bit shorter or slightly more written/formal in some contexts
• af því að is extremely common in everyday speech

Both are good, and both mean because here.

Because the sentence describes a current action based on an earlier result.

• Ég mæli hitann aftur = what the speaker is doing now
• hitamælirinn sýndi ekki mikinn hita = what the thermometer showed earlier

So the logic is:

1. The thermometer gave a reading.
2. That reading was not convincing or not high.
3. Because of that, the speaker is measuring again now.

This mix of tenses is completely normal.

That word order is very natural in Icelandic.

The clause begins with:

• Ég = subject
• mæli = finite verb

After that, Icelandic often places:

• the object: hitann
• then an adverb: aftur

So:

• Ég mæli hitann aftur

This is a normal, neutral way to say it.

You can move adverbs around in Icelandic, but that often changes emphasis or style. For example, putting aftur earlier can sound more marked. For a learner, Ég mæli hitann aftur is the safest and most natural pattern.

Yes. They are both forms of the noun hiti.

They differ because Icelandic changes nouns for:

• case
• definiteness

Here is what is happening:

• hitann = the temperature

  • accusative singular
  • definite

• hita = temperature / heat / fever

  • accusative singular
  • indefinite

So the sentence uses:

• hitann when referring to the specific temperature being measured
• hita when talking about the amount or degree shown by the thermometer

That difference is very natural in Icelandic, even if English often uses the same word form in both places.

Sýndi is the past tense, 1st/3rd person singular form of sýna, meaning show.

So:

• ég sýni = I show
• hann/hún/það sýnir = he/she/it shows
• hann/hún/það sýndi = he/she/it showed

Since the subject here is hitamælirinn = the thermometer, the meaning is:

• the thermometer showed

A useful thing to notice is that Icelandic past tense forms often do not look as predictable to English speakers as English showed, so it is worth learning verb forms individually.

The letter þ is pronounced like the th in think.

So:

• því begins with the same kind of sound as English th in thin, not the sound in this

Very roughly:

• þ = voiceless th
• ð = voiced th (like in this) in many contexts

So því starts with a thin/think type sound.