The proper word for first in Sindarin was minui
Sindarin
erui
adjective. first (incorrect use by the Gondorians)
er
adjective. single
erui
adjective. single, alone
minai
adjective. single, distinct, unique
er
single
1) er (pl. ir) (VT48:6), 2)
er
single
(pl. ir) (VT48:6)
erui
single
erui (first, alone). No distinct pl. form. 3) minai (distinct, unique), lenited vinai; pl. mini
erui
single
(first, alone). No distinct pl. form. 3) minai (distinct, unique), lenited vinai; pl. mini**
The proper word for first in Sindarin was minui