Questions & Answers about Þetta þunga sverð er mjög dýrt.
Why do we use þunga instead of the regular neuter form þungt?
The word þetta (this) acts as a trigger for the weak adjective declension. When an adjective comes between a demonstrative like þetta and a noun, it must take a weak ending. For a neuter noun in the nominative singular, that weak ending is -a, giving us þunga.
If þetta makes the adjective weak, why does dýrt have the strong neuter -t ending?
Only adjectives that are directly attached to the noun before the verb are affected by triggers like þetta. The adjective dýrt is on the other side of the verb er (is). Adjectives in this position always use the strong declension, which is why it takes the standard strong neuter ending -t.
Does the noun sverð (sword) need a definite ending here?
No. When you use a demonstrative pronoun like þetta (this) along with an adjective, the noun itself usually stays in the indefinite form. Þetta already points out exactly which sword we mean, so no extra definite ending is needed on sverð.
What clues in this sentence tell us the gender of sverð?