| Sg | Pl | |
| Nom | undirhyggja | undirhyggjur (rule) |
| Acc | undirhyggju (rule) | undirhyggjur (rule) |
| Dat | undirhyggju (rule) | undirhyggjum (rule) |
| Gen | undirhyggju (rule) | undirhyggna (rule) |
| Sg | Pl | |
| Nom | undirhyggjan (rule) | undirhyggjurnar (rule) |
| Acc | undirhyggjuna (rule) | undirhyggjurnar (rule) |
| Dat | undirhyggjunni (rule) | undirhyggjunum (rule) |
| Gen | undirhyggjunnar (rule) | undirhyggnanna (rule) |