Gnomish
cub
adjective. hollow
rothrin
adjective. hollow
tum
noun. hollow
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 word appearing as {tûm >>} tum “hollow” in the Gnomish Lexicon of the 1910s, an adjective form of G. {tum} tûm “valley” (GL/71). In Tolkien’s later writings, S. tum was only a noun.