A Vala, Lord of the Waters (S/26). This name was originally derived from his Valarin name or title Ul(l)ubōz (WJ/400). Later it was interpreted as a combination of the root √UL “pour” and the agental suffix -mo, thus meaning “Pourer”, and this interpretation influenced its final Quenya form (WJ/401).
Conceptual Development: The name ᴱQ. Ulmo appeared in the earliest Lost Tales as a replacement for very early ᴱQ. Linqil (LT1/58, 61), and the name kept this form in all of Tolkien’s later writings. At the earliest stage, ᴱQ. Ulmo appeared in the Qenya Lexicon as a derivative of the root ᴱ√ULU “pour, flow fast”, and in The Etymologies from the 1930s the name ᴹQ. Ulmo still had this derivation, from the root ᴹ√ULU “pour, flow”. The idea that his name was derived from Valarin did not emerge until the Quendi and Eldar essay from 1959-60 (WJ/400), but Tolkien retained the earlier derivation of his name as a false etymology.
Ulmo masc. name, used of the Vala of all waters (ULU), interpreted "the Pourer" by folk etymology, but the name was actually adopted and adapted from Valarin (WJ:400)