A noun appearing as N. rhui(w) “hunt, hunting” in The Etymologies of the 1930s derived from the root ᴹ√ROY “chase”, cognate to ᴹQ. roime (Ety/ROY¹). Here the initial r became voiceless rh as was usual in Noldorin, while it seems the medial m became w and then vanished.
Conceptual Development: The Gnomish Lexicon of the 1910s had similarly formed G. raust “hunt, chase”, clearly based on the early root ᴱ√RAVA that was the bases for “hunt” words in the contemporaneous Qenya Lexicon, as suggested by Christopher Tolkien (GL/65; QL/79; LT1A/Meássë).
Neo-Sindarin: Since the unvoicing of initial liquids did not occur in Sindarin, many people adapt this word as ᴺS. rui for purposes of Neo-Sindarin, as suggested in HSD (HSD). I would extend its meaning to “hunt, hunting, ✱chase”, to make it more distinct from “hunting” words based on [N.] fara-.
Earliest name of Taur-en-Faroth in Silmarillion drafts from the 1930s (SM/225). Its seems to be a combination of the plural of dôl “hill” and the form rewinion “of the hunters”, apparently a genitive plural formation, possibly related to N. rhui(w) “hunt” from the root ᴹ√ROY “chase” or perhap G. raust “hunt” from the root ᴱ√RAVA.