One of the greatest of the Maia, master of the seas that wash the shores of Middle-earth (S/30). His Quenya name is derived from his name in Valarin: Val. Oš(o)šai “spuming, foaming” (WJ/400).
Conceptual Development: This name dates back to the earliest Lost Tales, when ᴱQ. Osse was derived from the root ᴱ√’O’O along with other words related to the sea (LT1A/Ossë, QL/70). In The Etymologies, the name ᴹQ. Osse was derived from the primitive root ᴹ√GOS “dread” (Ety/GOS), perhaps referring to the awe-inspiring nature of the sea. The later derivation of Q. ëar “sea” < √GAY(AR) “awe, dread” was similar (PM/363, WJ/400).
In a list of roots written around 1959-60, Tolkien derived Ossë from an otherwised unattested root OS “making a hissing foaming noise” (PE17/138). His Valarin name did not appear until the Quendi and Eldar essay from this same period (WJ/400).
ossa noun "wall and moat" (LT2:336)