This is the 356th most frequent Icelandic word.
betri
"Betri" means "better" in English.
In this sentence, 'betri' is used as the comparative form of the adjective 'góður' (good), meaning 'better'. It describes the relative skill level of the subject compared to another person.
Hún er betri í skák en bróðir hennar.
She is better at chess than her brother.
Here, 'betri' is again the comparative form of the adjective 'góður'. It expresses a comparison of two days in terms of quality or positivity.
Ég vona að morgundagurinn verði betri en í dag.
I hope that tomorrow will be better than today.
In this context, 'betri' is used to compare the quality of possible solutions, implying a search for one that is more effective or appropriate.