A Maia, Lady of the Seas (S/30). The meaning of this name is unclear, and it is probably adapted from her Valarin title like the name of her spouse Ossë (WJ/404).
Conceptual Development: The earliest form of her name was ᴱQ. Ówen, from the “Poetical and Mythological Words of Eldarissa” (PME/70). A similar word ᴱQ. ówen “mermaid” appeared in the Qenya Lexicon as a derivative of the root ᴱ√’O’O “Sea” (QL/70). This name also appeared the earliest Lost Tales, but was quickly replaced ᴱQ. Ónen (LT1/58, 61). At this early stage, G. Uinen was the Gnomish equivalent of her name (GL/74), but Uinen gradually supplanted Ónen in the writing of the Lost Tales (LT1/121, 130 note #6).
In Silmarillion drafts from the 1930s, her name in Quenya was also ᴹQ. Uinen, and this name appeared in The Etymologies alongside N. Uinen as a combination of the roots ᴹ√UY “seaweed” and ᴹ√NEN “water” (Ety/UY, NEN). At this stage, the genitive form of her name was given as ᴹQ. Uinenden (Ety/UY) implying a stem form of Uinend-, but Tolkien may have abandoned this form, as evidenced by the later name Q. Uinéniel “Daughter of Uinen” (Uinen + -iel). The idea that her name was derived from Valarin did not emerge until the Quendi and Eldar essay from 1959-60 (WJ/404).
ui interjection "no" (originally an endingless negative verb in the 3rd person aorist: "it is not [so]"; see #u-). Apparently this is the word for "no" used to deny that something is true (compare vá, which is rather used to reject orders, or to issue negative orders). (VT49:28) Compare uito.