This is the 798th most frequent Icelandic word.
arnarfirði
"Arnarfirði" means "Arnarfjörður," which translates to "Eagle Fjord," a fjord in Iceland.
The word "Arnarfirði" is in the dative case here, "Arnarfirði", indicating a direction towards the place.
Ég fór í ferðalag til Arnarfjarðar.
I went on a trip to Arnarfjörður.
In this sentence, the word "Arnarfirði" is in the accusative case, "Arnarfjörð", as it represents the direct object of the sailing action.
Við sigldum yfir Arnarfjörð.
We sailed across the Arnarfjörður.
Here, "Arnarfjörður" is in the nominative case, referring to the subject of the sentence.