Questions & Answers about Súpan er köld.
Adjectives in Icelandic must agree with their nouns in gender, number and case. Here:
• kaldur is the masculine lemma “cold.”
• As a predicate adjective describing a feminine noun (súpa), it takes the feminine nominative singular form: köld.
• The vowel change a → ö is due to a regular historical sound change (i-umlaut) in the feminine form.