Breakdown of Hvers þunglyndi er þetta?
þetta
this
vera
to be
hver
who / what / which (one)
þunglyndið
the depression
Questions & Answers about Hvers þunglyndi er þetta?
Why do we use Hvers instead of Hver here?
Hvers is the genitive (possessive) case of the interrogative pronoun hver (who). In Icelandic, there is no separate vocabulary word for 'whose'; instead, you literally ask 'of whom' by putting hver into the genitive case.
Does hvers change its form to match the gender of the noun it owns?
How is the noun þunglyndi (depression) built?
It is a great example of literal Icelandic word-building! It combines the adjective þungur (heavy) and the noun lyndi (mood, disposition, or temper). So, depression is quite literally described as a 'heavy mood'.
Would we change þetta to þessi if the noun being asked about wasn't neuter?
No. In the common question structure Hvers ... er þetta? (Whose ... is this?), the word þetta acts as a general, independent pointer ('this thing here') rather than an adjective attaching directly to the noun. Therefore, it stays in the default neuter form þetta regardless of the noun's gender. It just happens that þunglyndi is also neuter!