This is the 511th most frequent Icelandic word.
húsið
"The house."
'Húsið' is the subject and refers to a specific house, functioning as the definite form of the noun "house".
Húsið er grænt.
The house is green.
'Húsið' represents the definite object of the prepositional phrase, indicating a specific house being entered.
Ég fór inn í húsið.
I went into the house.
'Húsinu' is in the dative case definite form, used after the preposition "á" (on) to denote location on a specific house.