Ég þræddi nálina í gær.

• Ég = I, the subject
• þræddi = the verb, past tense, threaded
• nálina = the direct object, the needle
• í gær = a time expression, yesterday

So the structure is:

subject + verb + object + time expression

The dictionary form is þræða, which means to thread.

In this sentence, þræddi is the past tense form. A learner will often want to memorize it like this:

• að þræða = to thread
• ég þræddi = I threaded

Because þræða is a weak verb, and its past tense is formed with -ði / -di / -ti depending on the verb.

For þræða, the past tense stem becomes:

• þræða → þræddi

This kind of consonant change is normal in Icelandic verb forms and is something you usually learn together with the verb rather than trying to predict perfectly every time.

Nálina is in the accusative singular definite.

That is because þræða takes a direct object, and direct objects are very often in the accusative in Icelandic.

So:

• nominative: nál
• accusative: nál
• accusative definite: nálina

In this sentence, nálina is the thing being threaded, so it appears as the accusative object.

In Icelandic, the definite article is usually attached to the end of the noun instead of being a separate word.

So:

• nál = needle
• nálin = the needle
• nálina = the needle, in the accusative case

That -ina ending includes both:

• the noun ending needed here
• the definite article

This is a very common feature of Icelandic nouns.

Nálina means the needle, so it sounds like a specific needle, probably one already known from context.

You could use an indefinite form in some contexts, but Ég þræddi nál í gær sounds less natural as a basic sentence. More natural indefinite versions would usually need a fuller phrase, such as something equivalent to a needle in a context where that matters.

In practice, þræða nálina is a very natural way to say thread the needle, especially when talking about a particular needle in front of you.

Í gær is the normal Icelandic expression for yesterday.

Even though í often means in, the whole phrase í gær should be learned as a fixed time expression. You generally do not translate it word-for-word.

So just remember:

• í dag = today
• í gær = yesterday
• á morgun = tomorrow

Yes. That is a very natural alternative.

If you move í gær to the front for emphasis, Icelandic uses verb-second word order, so the verb comes next:

• Ég þræddi nálina í gær.
• Í gær þræddi ég nálina.

Both are correct. The second version puts more focus on yesterday.

That is much less natural in ordinary Icelandic.

The most neutral orders are:

• Ég þræddi nálina í gær.
• Í gær þræddi ég nálina.

Putting í gær between the verb and object is possible only in more marked or special contexts, but it is not the normal beginner pattern to imitate.

Þ is pronounced like th in English think, not like th in this.

So þræddi begins with the voiceless th sound.

Also:

• þ = unvoiced, like think
• ð = voiced, like this or a soft th sound

This contrast is very important in Icelandic spelling.

A helpful rough guide for English speakers is:

THREH-dee or THRYEH-dee, depending on how fine you want the vowel quality

A few details:

• þr is a real consonant cluster: say th and then an r
• æ is a front vowel, somewhat like the vowel in my in some descriptions, but the exact Icelandic sound is different
• dd here does not mean you hold the sound twice the way English spelling might suggest; it is just part of the Icelandic spelling and morphology

The safest approach is to listen to native audio and imitate the rhythm.

Usually, ég is kept.

Icelandic does have rich verb inflection, but subject pronouns are still commonly expressed in normal speech and writing. So:

• Ég þræddi nálina í gær is the normal full sentence.

You may occasionally see omitted subjects in informal notes, diaries, or special styles, but as a learner, it is best to include ég.

Nál is a feminine noun, and yes, that matters.

Gender affects:

• the form of the definite article
• adjective endings
• some case forms

For nál, some useful forms are:

• nominative singular: nál
• accusative singular: nál
• nominative definite: nálin
• accusative definite: nálina

So the feminine gender helps explain why the definite accusative form looks the way it does.

Yes. It is a completely normal and natural Icelandic sentence.

It uses:

• ordinary subject-verb-object order
• a common past-tense form
• a standard time expression at the end

So it is a good model sentence for learning several basic Icelandic patterns at once.