An occasional feminine suffix in Sindarin, in one place given as a feminine patronymic (PE17/170) as in the name Lúthien “Daughter of Flowers” (PE17/15, 161). See the entry on the root √YE(L) for a discussion of conceptual vacillations on its connection to “daughter”.
Conceptual Development: In Noldorin it seems N. -ien was simply a feminine suffix in the name N. Lhúthien “Enchantress” (Ety/LUK).
pl1. -is suff. fem. ending referring to persons or animals used after dh [= ð], th. >> -eth, -on