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.