A Noldorin name for Ilk. Umboth Muilin in Silmarillion drafts from the 1930s, translated “Pools of Mist” (LR/262, footnote). In The Etymologies it was given as a combination of hîth “mist” and the lenited class-plural of lhîn “pool” (Ety/KHIS).

See S. Aelin-uial for further discussion.