Aragorn’s horse (LotR/778), translated “Horse of the Lady” (SA/roch) or “Steed of the Lady” (PE17/97), a combination of roch “horse” and heryn “lady” (PE17/97), with the [[s|[x] (“ch”) softening to [h] in Gondorian pronunciation]].
Conceptual Development: In Lord of the Rings drafts from the 1940s, this name was already N. Roheryn (WR/435). The name also appeared in The Etymologies from the 1930s beside an older form Rocheryn (EtyAC/KHER).
prop. n. 'Steed of the Lady', Aragorn's steed given him by Arwen. Softened Gondor form of pure S. Roch(ch)eruin > Rocheryn for Roch e Cheruin. >> Roch e Cheruin, Rocheruin, Rocheryn