Old Norse/Grammar/Adjectives and Adverbs

Strong Adjective Declension
Singular Plural
Case Masculine Neuter Feminine Masculine Neuter Feminine
Nominative -r -t -(u-umlaut) -ir -(u-umlaut) -ar
Genitive -s -s -rar -ra -ra -ra
Dative -um -u -ri -um -um -um
Accusative -an -t -a -a -(u-umlaut) -ar
Weak Adjective Declension
Singular Plural
Case Masculine Neuter Feminine Masculine Neuter Feminine
Nominative -i -a -a -u -u -u
Genitive -a -a -u -u -u -u
Dative -a -a -u -um -um -um
Accusative -a -a -u -u -u -u

Note the weak declension here, neuter is always 'a.' Masculine is 'i' in the nominative, but 'a' elsewise. The plural is 'u' except the dative 'um' ending.