The Ilkorin word for “one” attested only in the name Ermabuin or Ermab(r)in “One-handed” (Ety/MAP).
Doriathrin
ermabuin
masculine name. One-handed
er Reconstructed
cardinal. one
gelion
adjective. bright
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.
Predecessor to the name S. Erchamion. In The Etymologies, the form Ermab(r)in “One-handed” was marked Ilkorin (Ety/MAP), and the similar form Ermabuin from the narratives may also be Ilkorin, since it appeared beside the Ilkorin name Mablosgen “Empty-handed” (LR/131). This name is a compound of er “one”, mâb “hand” and a variation of the adjective suffix -en. The u might be explained as a fossilized dual element [u], but the absence of this vowel in The Etymologies may mean that Tolkien rejected it in the Ilkorin form of the name.