Gnomish
bi
preposition. in
gwi-
prefix. twi-, bi-, di-
ba
preposition. in
atha
cardinal. two
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.
A preposition for “in” in the Gnomish Lexicon of the 1910s (GL/21). With the article it has the form bi- and without the article b’- or ba, presumably pre-vocalic and pre-consonantal. It was equivalent to ᴱQ. ve “as, like”, which in the contemporaneous Qenya Lexicon was derived from the early root ᴱ√VĪ “as” (QL/101). On other pages of the Gnomish Lexicon Tolkien previously had G. avin “into”, G. bi “in”, G. bin “into”, and G. bir “in, within, inside”, all deleted but more in keeping with the Qenya Lexicon root (GL/20, 22).