@@@ dual and plural forms representative of nouns in the same class
Qenya
ilmen
place name. Place of Light
ilmen-assa
place name. Chasm of Ilmen
earendel
masculine name. Earendel
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
In Silmarillion drafts from the 1930s, the gap beside the world through which the Sun and Moon traveled when they were not visible in the sky (SM/237, 240), also appearing in The Etymologies as compound of Ilmen and assa “hole” (Ety/GAS).