Earlier name of S. Aelin-uial in The Etymologies from the 1930s (Ety/AY) appearing along with variants Elinuial (Ety/KHIS, MBOTH, MUY) and Lhîn Uial (Ety/MUY). All these names contain uial “twilight” as well as a word for “pools”, either the plural of oel or (plural?) lhîn. In the narratives of this period, however, the name already appeared in its later form Aelin-uial (LR/262).
Sindarin
Umboth Muilin
noun. veiled pool
umboth (Dor. “large pool”) + muilin (Dor. “secret, veiled”)