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).
The meaning "he" is deduced from the apparent function of this word in the so-called "King's Letter", but it also seems possible to interpret it as "indeed" (as in Q. e, LR/63, VT/45:11), used here in a way of formal address expressing the wishes or the will of the King