A verb in the Qenya Lexicon of the 1910s appearing as ᴱQ. sisi- “scorch, singe, fry” derived from the early root ᴱ√SISI “singe, etc.” (QL/84). The root’s likely Gnomish derivatives such as G. thista- “dry up” (GL/73) indicate the root form is probably *ᴱ√ÞISI.

Neo-Quenya: I think this word is worth salvaging as Neo-Quenya ᴺQ. sis-, though it would need to be derived from a Neo-Root ᴺ√THITH to retain this same form.