This is the 397th most frequent Icelandic word.
degi
The word "degi" is the dative singular form of "dagur," which means "day" in English.
'Day' (dagur in nominative case) is the subject of this sentence, denoting the current day being described.
Dagurinn er fallegur í dag.
The day is beautiful today.
Here, 'deginum' is in the dative case, showing the object affected by the action of wasting the day.
Við höfum enga afsökun fyrir því að eyða deginum illa.
We have no excuse for wasting the day poorly.
In this sentence, 'degi' is in the dative case, indicating time location of an event taking place on a specified day.