Of mikil streita getur valdið höfuðverk.

Of means too, excessively, so of mikil streita means too much stress or excessive stress.

Without of, mikil streita would mean great stress, a lot of stress, or severe stress, but not necessarily too much. So of adds the idea of excess.

A useful contrast is:

• mikil streita = a lot of stress / great stress
• of mikil streita = too much stress

No. Icelandic of is a completely different word from English of.

In this sentence, of is an adverb meaning too or overly.

It is also different from Icelandic af, which often means of, from, off, depending on context. Learners often mix up of and af, but they are different words with different meanings.

Because mikil has to agree with streita.

Streita is:

• feminine
• singular
• nominative here, because it is the subject

So the adjective must also be feminine singular nominative:

• masculine: mikill
• feminine: mikil
• neuter: mikið

That is why the sentence has of mikil streita.

Getur is the 3rd person singular present tense of geta.

So it matches the singular subject of mikil streita:

• ég get = I can
• þú getur = you can
• hann/hún/það getur = he/she/it can

Here the subject is a singular noun phrase, so getur is the correct form.

After geta, Icelandic does not use að before the following verb form.

So you say:

• getur valdið
• not getur að valdið

This is similar to how English says can cause, not can to cause.

It is not past tense here.

After geta, Icelandic commonly uses a non-finite verb form often called the supine (sagnbót). For valda, that form is valdið.

So:

• geta valdið = can cause
• hefur valdið = has caused

The tense of the sentence comes from getur, which is present tense. So the whole sentence is present in meaning: can cause.

This is a very common pattern in Icelandic, so it is worth getting used to.

The dictionary form is höfuðverkur.

But the verb valda takes the dative case, so the noun changes form:

• nominative: höfuðverkur
• dative: höfuðverk

So in this sentence, höfuðverk is there because of the verb valda.

A very important point for learners: valda + dative

Because Icelandic does not have an indefinite article like English a/an.

So a bare noun can mean:

• a headache
• headache in a general sense

If you wanted the headache, Icelandic would usually add the definite article to the end of the noun:

• höfuðverkur = a headache / headache
• höfuðverkurinn = the headache

Mostly can.

In a sentence like this, getur expresses possibility: excessive stress is capable of causing headache. In natural English, this can sometimes also be translated as may cause, especially in medical or formal wording.

So the Icelandic meaning is roughly in that range:

• can cause
• sometimes naturally rendered as may cause

This is the normal, neutral order:

• subject: Of mikil streita
• finite verb: getur
• rest of the predicate: valdið höfuðverk

So the structure is basically:

Of mikil streita + getur + valdið höfuðverk

Icelandic word order is somewhat flexible, but this version is the straightforward, natural one for a learner to use.

Yes, usually.

Streita is normally used as a mass/uncountable noun, much like English stress. So Icelandic commonly uses the singular when speaking about stress in general.

That is why the sentence uses singular agreement:

• streita
• getur

not a plural form.