Learn Hardcore Icelandic: Hún syngur fallega.

Hún is the nominative (subject) form of the feminine pronoun—She. Hana is the accusative or dative form, used when “her” is an object or after certain prepositions. Since Hún here is doing the singing (the subject), you must use the nominative Hún.

Why does the verb end in -ur (i.e. syngur)?

Icelandic verbs attach -ur in the 3rd person singular present tense for most conjugation classes. Syngja (“to sing”) is a strong verb whose present stem is syng-, so you add -ur to get syngur = “he/she sings.”

How do you get the adverb fallega from the adjective fallegur?

Adverbs from adjectives ending in -ur, -ir or -ar are formed by dropping that ending and adding -lega.
• fallegur → remove -ur → falleg- → add -lega → fallega (“beautifully”).

Does fallega change for gender, number or case like adjectives?

No. Once you form an adverb (here fallega), it is indeclinable. Adverbs in Icelandic do not agree with nouns; they remain the same in every context.