Quenya has a definite article i = "the", e.g. i eleni "the
stars" in Namárië. There is no indefinite article like
English "a, an"; the absence of the article i usually indicates
that the noun is indefinite: Elen "star" must be translated "a star"
when English grammar requires an article, as in the famous greeting Elen
síla lúmenn' omentielvo "a star shines
at the hour of our meeting" (LotR1/I ch. 3). But sometimes Tolkien's translations
introduce a "the" where there is no i in the original, cf. the first
line of Namárië: Ai! laurië lantar lassi...
"Ah! like gold fall the leaves..." rather than just "(some) leaves".