Gnomish
umbel
noun. a dell
umli
noun. a dell
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.
umbel
noun. a dell
umli
noun. a dell
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 glossed “a dell” in the Gnomish Lexicon of the 1910s with variants umbel and umli, apparently an elaboration on G. um “lowlying” (GL/74).