Gnomish
glissith
noun. sugar
glist
noun. sugar
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.
In the Gnomish Lexicon of the 1910s the word for “sugar” was G. glist along with a longer variant G. glissith where the second element was G. thith “dust” (GL/39). The word glist was likely derived from the early root ᴱ√LISI “sweetness” (QL/54-55).
Neo-Sindarin: Since √LIS survived as the basis for “sweet” words in Tolkien’s later writings, I’d retain ᴺS. glist “sugar” for purposes of Neo-Sindarin.