Learn Icelandic: Þetta er mjög dularfullur sjúkdómur.

The suffix -dómur creates masculine abstract nouns, usually indicating a state, condition, or domain. Here, it is added to the root of the adjective sjúkur (sick). Together, it forms sjúkdómur, literally meaning the condition of being sick, which translates to a disease.

Why do we use the neuter pronoun þetta (this) when the noun sjúkdómur is masculine?

When introducing or identifying something with 'This is...', Icelandic uses the neuter pronoun þetta as a fixed dummy subject, regardless of the gender of the noun being introduced. However, notice that the adjective dularfullur (mysterious) still correctly takes the masculine nominative ending -ur to agree with the masculine noun sjúkdómur.

How is the adjective dularfullur constructed?

It is made of the noun dul (secrecy, concealment) and the common suffix -fullur (full of). When combining them, the first word takes its genitive singular form, dular-, making the literal meaning 'full of secrecy'.

How would the phrase change if we were talking about 'the' very mysterious disease?