Qenya
onas(se)
adverb. [in/at] the same place
on-
prefix. the same (oneness, uniqueness), identical
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.
The correlatives ᴹQ. onosse “[in/at] the same place”, onas(se), or (archaic) †osse appeared in Demonstrative, Relative, and Correlative Stems (DRC) from 1948 (PE23/100, 111), a combination of ᴹQ. on- “same” and the locative suffix ᴹQ. -sse.
Neo-Quenya: For purposes of Neo-Quenya I would update this to ᴺQ. imassë “in/at the same place” using im- “same”.