Learn Hardcore Icelandic: Bíllinn er bilaður.

Icelandic attaches its definite article to the end of the noun as a suffix. For masculine singular nouns in the nominative case, that suffix is -inn. So bíll (“car”) becomes bíllinn (“the car”).

What part of speech is bilaður in Bíllinn er bilaður, and why is the past participle used here?

Bilaður is the past participle of the verb bila (“to break down”). In this sentence it functions as an adjective describing the resulting state of the car—“broken” or “defective.” Using vera (“to be”) plus a past participle is how Icelandic expresses a state that has resulted from an action, much like “the car is broken” in English.

Why does bilaður end in -ður, and could that ending ever be different?

Because bíllinn is definite, the adjective (here the participle) follows the weak declension pattern. For masculine singular nominative, the weak ending is -ður. In other genders or numbers (or with an indefinite noun), participle endings change—for example neuter singular becomes -að, feminine singular -uð, and plurals -dir/ðar/ð, depending on gender.

How would bilaður change if the subject were a neuter noun, for example reiðhjólið, the bicycle?