Learn Hardcore Icelandic: Hún er veik í dag, ekki satt?

It literally means not true?, used like English right? or isn’t that so? after a statement to seek confirmation. So the whole sentence is a statement (She is sick today) plus a confirmation tag (right?). It’s common and natural in everyday Icelandic.

How do I answer this tag—do I use já, jú, or nei?

To agree with the positive statement, say Já (Yes): Já, hún er það / Já, hún er veik.
To disagree, say Nei (No): Nei, hún er ekki veik í dag.
Use Jú specifically to contradict a negative question or statement. Example: Er hún ekki veik í dag? — Jú, hún er veik. Here, because the main clause is positive, Já is the natural agreement.

Why is it veik and not veikur or veikt?

Adjectives agree with the subject in gender and number. Hún is feminine singular, so the predicate adjective is feminine singular: veik. Masculine would be veikur (e.g., Hann er veikur), and neuter veikt (e.g., Það er veikt).

What exactly is í dag, and why is dag in that form?

Í dag means today. The preposition í can govern accusative or dative; in time expressions like this it takes the accusative. Dag is the accusative singular of dagur (day). It’s a fixed, very common phrase.

Can I put the time first? For example, Í dag er hún veik, ekki satt?

Yes. Icelandic is verb-second (V2): if you front í dag, the finite verb er must still be in second position: Í dag er hún veik, ekki satt? This is perfectly natural and slightly emphasizes the time.

Could I ask the same thing with a direct yes/no question instead of a tag?

Yes:

Neutral question: Er hún veik í dag?
Negative question (expecting “yes”): Er hún ekki veik í dag? If you confirm, use Jú: Jú, hún er veik.

Why is there a comma before ekki satt??

A sentence-final tag is separated by a comma in Icelandic: main clause, then comma, then the tag (..., ekki satt?). That’s the standard punctuation.

What does satt agree with here?

Satt is the neuter form of the adjective sannur (true). In the fuller form Er það ekki satt? (Is that not true?), það (it/that) is neuter, so the adjective is neuter. The shorter ekki satt? keeps that neuter agreement implicitly.

Where does ekki go if I want to negate the main clause?

Place ekki after the finite verb:

Hún er ekki veik í dag. If you front the time:
Í dag er hún ekki veik. In a yes/no question, it follows the verb as well:
Er hún ekki veik í dag?

Are there other natural tag options besides ekki satt??

Yes, common alternatives include:

..., er það ekki? (isn’t that so?)
..., ekki? (right?)
..., eða hvað? (or what?) All seek confirmation, with ekki? being very colloquial and er það ekki? a bit more explicit.

Pronunciation tips for each word?

Hún: roughly “hoon” (long u sound).
er: short “ehr”.
veik: like “vake” (ei as in “vein”; final k crisp).
í: “ee” (long i).
dag: “daag” with a soft/voiced g at the end.
ekki: “EH-ki” with a clear double k.
satt: “saht” with a strong, long t. Stress is on the first syllable of each word.

Is veik always the right word for “sick”? What about other options and genders?

veikur/veik/veikt = sick/ill (general). Use the form that matches gender/number: Hann er veikur, Hún er veik, Barnið er veikt.
lasinn/lasin/lasið = ill, under the weather (often about a temporary ailment): Hún er lasin.
slappur/slöpp/slappt = weak, run-down.
sjúkur/sjúk/sjúkt can mean seriously ill, and also “addicted/crazy about” in some contexts. In your sentence, veik is the neutral, standard choice.

Can I say Hún er veik í dag? with rising intonation to make it a question?

In informal speech, yes—it works as an echo/confirmation question. The standard way, though, is inversion: Er hún veik í dag? The tag version Hún er veik í dag, ekki satt? is also very natural when you expect agreement.

What are the case forms of hún I should know?

Nominative: hún (she) — subject form, as in the sentence.
Accusative: hana (her) — Ég sé hana (I see her).
Dative: henni (to her) — Ég gaf henni blóm (I gave her flowers).
Genitive: hennar (her/hers) — bíll hennar (her car).

Any tip about intonation on the tag ekki satt??

Use falling intonation if you’re fairly sure and just seeking confirmation (more like English “right.”), and a rising intonation if you’re genuinely asking (more like “right?”). Both are possible depending on your expectation.