Learn Icelandic: Þriðja hæðin er lokuð.

In Icelandic, ordinal numbers like 3rd, 4th, and 5th act like adjectives and must match the gender of the noun. Hæð (floor) is a feminine noun, so we use the feminine nominative form þriðja. For a masculine noun, it would be þriðji.

I see hæðin means "the floor". Why don't we use the free-standing word for "the" (hin) like we normally do before weak adjectives?

Great catch! Usually, when you put a weak adjective before a definite noun, you use a separate word for "the" (like hin stóra hæð). However, ordinal numbers are a special exception. You just put the ordinal directly in front of the noun with its attached article to get þriðja hæðin.

Why does the word lokuð end in -uð?

Lokuð (closed) is an adjective describing the feminine noun hæðin. Adjectives need to match the gender of the noun they describe. The dictionary form (masculine) is lokaður, but the ending changes to match the feminine nominative form, becoming lokuð.

Does the word þriðja change if we use a different grammatical case?