A noun appearing as G. siel “granddaughter” in the Gnomish Lexicon of the 1910s, a feminine variant of sion “grandson” (GL/67).

Neo-Sindarin: Since there are no other attested alternatives, I would use ᴺS. siel for “granddaughter” in Neo-Sindarin, as a now-obscure modification of S. -iel “daughter”.