In Sindarin, there is no indefinite article like English "a, an" when there is no definite article, that means that it is indefinite:

        Edhel = "Elf " or "an Elf "

The article use in Sindarin is "i" it is like "the" in English, there is a plural form to this article that we don’t retrieved in English "in"

        The king------->I aran
        The kings------>In erain

The article can be suffixed to the prepositions (-n, -in )

        Be (according to)------->Ben (according to the/ in the)
        Na (toward, at, to)------>Nan (toward the, at the, to the)
        O (from/of)-----------> Uin (from the/of the)
        Or (on)-------------->Erin (on the)
        Nu /No (under)-------->Nuin (under the)

Exercises

Complete the sentences with the good article.

1) According to the annals---->­ (______) ìnias

2) The feast ----> (_______) mereth

3) The blood ----> (_______) iâr

4) Annals of the king ----> ìnias (_______) aran

5) Look toward the Sun----> Tiro (_______) Anor

6) On the bed----> (______) haust