ᴺS. [N.] ^rŷn n. “chaser, hound of chase” (Category: Dog)
The word N. rhŷn “‘chaser’, hound of chase” appeared in The Etymologies of the 1930s derived from primitive ᴹ✶ronyō under the root ᴹ√ROY¹ “chase” (Ety/ROY¹). It is not entirely clear how the ŷ arose in this word; compare N. rhein < rhœin (< *ronya) < ᴹ✶runya (Ety/RUN) which shows the more typical Noldorin phonetic developments. Perhaps it was a dialectical development, or was based on a variant primitive form ronı̯- with early o-loss.
Reference ✧ Ety/ROY¹ ✧ “‘chaser’, hound of chase”
|ᴹ✶ronyō > rhŷn||[ronjō] > [ronjo] > [ronio] > [rœnio] > [rœni] > [rœin] ? [ryn] > [r̥yn] > [r̥ȳn]||✧ Ety/ROY¹|