√DUY root. “flow (strongly), flood, drench, inundate, pour”
A root variously glossed as “flow (strongly)” or “flood, drench, inundate”, its most notable derivative is S. duin “(large) river”, which is an element in many river names such as S. Anduin or S. Baranduin. Its first precursor seems to be primitive ᴱ√dui mentioned in Gnomish Lexicon of the 1910s as the basis for words like G. duif “stream” but also G. duil “flight” (GL/31, 45), so perhaps meaning “flow” in both water and air.
It appeared in The Etymologies of the 1930s as ᴹ√DUI̯, mostly with Ilkorin derivatives though Tolkien noted it was also used in Noldorin (Ety/DUI; EtyAC/DUI). The root dui- appeared again in Tolkien’s 1967 notes on the Nomenclature of the Lord of the Rings, again as the basis for S. duin; in these notes he specified that its Quenya equivalent Q. luine was not used (RC/766).
Tolkien mentioned this root again in some 1968 etymological notes, where he said that other Quenya derivatives like Q. luimë “flood” and luita- “to flood” did survive (VT48/23). When Tolkien first wrote this note, he considered but rejected having a Q. form nuine “river” (VT48/30), perhaps by assimilation of the initial d- to the following n. Despite the repeated rejection of the Quenya cognate of S. duin, it does appear in a couple Quenya river names, such as Q. Anduinë and Nunduinë, so perhaps it survived in compounds as suggested by Patrick Wynne (VT48/30-31, note #6) or was restored as a late borrowing from Sindarin.
References ✧ RC/766; VT48/23-24, 26, 30
ᴹ√DUY root. “*flow”
References ✧ Ety/DUI, GWEN; EtyAC/DUI
Reference ✧ GL/45 ✧ dui