Primitive form given as khrassê, derived from a stem KHARÁS (LR:363) that is not defined, but compared to a stem KARAK "sharp fang, spike, tooth" (LR:362). The form khrassê displays the loss of an unaccented stem-vowel often seen in primitive words (cf. for instance d'râk- "wolf" from DARÁK-); the ending -ê is found on a number of words denoting inanimates (though it is also a feminine ending). For the doubling of the final s, compare lassê "leaf" from LAS1 (LR:367).
This hr- is our only example of how primitive khr- comes out in Nandorin; hr is surely meant to denote an unvoiced r, as in Tolkien's later spelling of Quenya words (e.g. hroa "body"). For primitive -ê becoming Nandorin -a, compare cwenda (q.v.) from kwenedê.
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.