Questions & Answers about Þetta eru mjög gamlir hlutir.
Why do we use þetta (this) when the sentence means 'These are'?
How do we get the plural form hlutir?
The singular word is hlutur (thing), which is a masculine noun. To make it plural in the nominative case, we drop the standard masculine -ur ending and replace it with the plural ending -ir, giving us hlutir.
Why is the word for 'old' written as gamlir here?
Adjectives must match the noun they describe in gender and number. Since hlutir is a masculine plural noun, the dictionary form of the adjective gamall (old) changes to its masculine plural form, gamlir.