Gnomish
sion
noun. grandson
nion
noun. grandson
Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!
sion
noun. grandson
nion
noun. grandson
A noun appearing as G. sion “grandson” in the Gnomish Lexicon of the 1910s (GL/67), probably related to ᴱQ. yó or yond- “son” in the Qenya Lexicon (QL/106), though where the initial s came from is unclear.
Neo-Sindarin: Since there are no other attested alternatives, I would use ᴺS. sion for “grandson” in Neo-Sindarin, as a now-obscure modification of S. -ion “son”.