A noun in The Etymologies of the 1930s gloss “precipice”, derived from primitive ᴹ✶khrassē (Ety/KHARÁS). Tolkien listed two soft mutated forms: i-rass and (archaic) †i-chrass, the latter the proper historical development but the former reformed to match normal (Noldorin) patterns of mutation.
Neo-Sindarin: This word would remain rhass if adapted into Sindarin, as its ancient initial consonants khr- would still produce rh-. But its mutations would likely be different; see the discussion of the Sindarin soft mutation.
The form rhaes in the Etymologies is a misreading according to VT/46:10