önnur

In a sentence

• Ég hef þegar lesið þessa bók, en mig langar að lesa einhverjar aðrar.

  I have already read this book, but I want to read some others.

  Here, 'aðrar' refers to OTHER books, emphasizing a substitution or competitive characteristic.

• Ein stígvél var of lítil, og hin hitt var önnur.

  One boot was too small, and the other was different.

  In this case, 'önnur' indicates being OTHER in terms of contrast or distinction.

• Hún hafði öll önnur verk, en kemur síðan að þessu.

  She had all other tasks, but now she comes to this one.

  The usage of 'önnur' denotes all others in the set of tasks, distinguishing them from the current one.