Middle Primitive Elvish
sus
root. hiss
sis
root. hiss
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 root in The Etymologies of the 1930s glossed “hiss” with the derivative ᴹQ. surya “spirant consonant” (Ety/SUS). The root ᴹ√SIS was written nearby and was likely intended to be a variant as suggested by Carl Hostetter and Patrick Wynne (EtyAC/SIS). These two variants might be later iterations of primitive ᴱ✶sṣt- from the Early Noldorin Dictionary of the 1920s with derivatives like ᴱQ. histe- “hiss” (PE13/163).