Nálin er lítil, og þráðurinn er svo dökkur að ég sé hann varla.

Both words have the definite article attached to the end, so they mean the needle and the thread.

• nál = needle

• nálin = the needle

• þráður = thread
• þráðurinn = the thread

Icelandic usually adds the as a suffix instead of using a separate word. The exact ending changes depending on the noun’s gender, number, and case. Here:

• -in fits nál as a feminine singular nominative form
• -inn fits þráður as a masculine singular nominative form

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

Here:

• nálin is feminine singular nominative, so lítill becomes lítil
• þráðurinn is masculine singular nominative, so dökkur stays dökkur

So:

• lítil = feminine singular nominative of lítill
• dökkur = masculine singular nominative of dökkur

This is a very important difference from English, where adjectives do not change form.

Svo ... að means so ... that.

So:

• svo dökkur að ég sé hann varla
  = so dark that I can hardly see it

This is a common Icelandic pattern for showing result or consequence:

• Hann er svo þreyttur að hann sofnar strax.
  = He is so tired that he falls asleep immediately.

Here sé is from sjá and means I see.

The verb sjá is irregular in the present tense:

• ég sé = I see
• þú sérð = you see
• hann/hún/það sér = he/she/it sees

So in this sentence:

• ég sé hann varla = I hardly see it / I can hardly see it

This can confuse learners because sé can also be a form of vera in other contexts, but here it clearly belongs to sjá.

Because English often uses can with verbs of perception, while Icelandic often does not need it.

So:

• ég sé hann varla
  literally: I hardly see it
• natural English: I can hardly see it

The Icelandic sentence is perfectly normal without geta (can / be able to). Adding geta here would usually sound less natural unless you specifically want to stress ability.

Because Icelandic pronouns follow grammatical gender, not natural gender.

The noun þráður is masculine, so when you refer back to it, you use the masculine pronoun:

• hann

Even though English would say it, Icelandic uses the pronoun that matches the noun’s gender.

So:

• þráðurinn = masculine
• therefore hann = it here

In this sentence, hann does not mean a male person. It just refers to the masculine noun þráðurinn.

Varla means hardly, barely, or scarcely.

So:

• ég sé hann varla = I can hardly see it
• literally: I see it barely

It often gives the sentence a kind of almost not meaning. It is stronger than just saying something is difficult; it suggests it is only just possible, or almost impossible.

Because after að, Icelandic normally uses subordinate clause word order, where the subject comes before the verb.

So:

• að ég sé hann varla = that I hardly see it

This is different from the main-clause verb-second pattern that Icelandic often uses.

Very roughly:

• main clause: the finite verb tends to come early
• subordinate clause after að: subject + verb is the normal pattern

So að ég sé ... is exactly what you should expect.

The main noun phrases are in these cases:

• nálin — nominative, because it is the subject of er
• þráðurinn — nominative, because it is also the subject of er
• hann — accusative object of sjá

The adjectives also match the nominative subjects:

• lítil agrees with nálin
• dökkur agrees with þráðurinn

A small detail: the masculine pronoun hann looks the same in both nominative and accusative, so you identify its role from the sentence structure and from the fact that sjá takes an object.

They are two very important Icelandic letters:

• þ is like th in thin
• ð is like th in this (though in Icelandic it can be softer or weaker depending on position)

So in this sentence:

• þráðurinn begins with þ, so the first sound is like th in thin
• the ð in þráðurinn is voiced, like th in this

English speakers usually need some practice with these, but those rough comparisons are a good start.

Yes. In this sentence dökkur describes the thread’s color or visual appearance: dark.

Because it agrees with þráðurinn, it appears in the masculine singular nominative form dökkur. If it described a feminine noun, you would expect a different form, and likewise for a neuter noun.

So the important thing here is not just the meaning dark, but also the fact that the adjective changes form to match the noun.