The form rhaes in the Etymologies is a misreading according to VT/46:10
Sindarin
rass
horn
ras
noun. horn (especially on living animal, but also applied to mountains)
ras(s)
noun. horn, horn [of both animals and mountains]
A noun for “horn” appearing in notes on the name Caradhras “Redhorn” from the 1950s or 60s (PE17/36). This word was an element in other names as well, such as Methedras “Last Peak” and Nimras “White Horn”.
Conceptual Development: This word appeared as N. rhas “horn” in The Etymologies of the 1930s under the root ᴹ√RAS “stick up” (Ety/RAS). Christopher Tolkien gave it as rhaes in The Etymologies as published in The Lost Road (LR/383), but Carl Hostetter and Patrick Wynne corrected this to rhas in their Addenda and Corrigenda to the Etymologies (VT46/10). In The Etymologies it appeared beside an alternate form N. rhasg, equivalent to ᴹQ. rasko (Ety/RAS; EtyAC/RAS).
Neo-Sindarin: Some Neo-Sindarin writers adapt its variant form as ᴺS. rasg, but I recommend sticking to attested S. ras(s) for a “horn” of both animals and mountains.
rasg
noun. horn (especially on living animal, but also applied to mountains)
caran-rass Archaic
place name. Redhorn
The archaic form of Caradhras; see that entry for further discussion.
rass
horn
(mountain peak), pl. #rais (idh rais). The pl. is attested in the name Ered Nimrais. Side-form rasc, rasg.
rhass
precipice
rhass (i rass for ”older” i** **chrass; construct rhas), pl. rais (?idh rais).
rhass
precipice
(i rass for ”older” i chrass; construct rhas), pl. rais (?idh rais).
rasg
noun. horn
rom
horn
- rom (trumpet), pl. rym (idh rym), coll. pl. rommath. (Cf. also romloth ”horn-flower”, tobacco.) 2) rass (mountain peak), pl. #rais** (idh rais). The pl. is attested in the name Ered Nimrais. Side-form rasc, rasg. 3) rafn (wing, extended point at the side), pl. raifn (idh raifn); 4) tarag (i darag, o tharag), pl. teraig (i theraig**). The word may be used of a ”steep mountain peak” (VT46:17; ”steep mountain path” in LR:391 is a misreading).
avras
noun. precipice
A noun glossed “a precipice” in notes from the late 1960s (PMB), given as a derivative of the root √BARAS (PE17/22-23).
caradhras
place name. Redhorn
Sindarin name of a peak in the Misty Mountains translated “Redhorn”, itself a translation of Kh. Barazinbar of the same meaning (LotR/283). This name is a combination of caran “red” and ras(s) “horn”, with the dh appearing because [[s|[nr] became [ðr]]] in the phonological history of Sindarin (LotR/1113, PE17/36).
Conceptual Development: In Lord of the Rings drafts from the 1940s, Tolkien first considered and rejected the names N. Bliscarn and N. Carnbeleg before settling on N. Taragaer “Ruddyhorn” (RS/419, 433), with Taragaer also appearing in The Etymologies (Ety/TARÁK). In these early drafts, Tolkien also considered the names N. Caradras and Rhascaron (RS/433), and he eventually switched to Caradras >> Caradhras (TI/166), keeping the final name thereafter.
rom
noun. horn, trumpet
rafn
horn
(wing, extended point at the side), pl. raifn (idh raifn)
rom
horn
(trumpet), pl. rym (idh rym), coll. pl. rommath. (Cf. also romloth ”horn-flower”, tobacco.)
rû
sound of horns
pl. rui (idh rui), also romru, pl. remry (idh remry) for archaic römry
tarag
horn
(i darag, o tharag), pl. teraig (i theraig). The word may be used of a ”steep mountain peak” (VT46:17; ”steep mountain path” in LR:391 is a misreading).
till
sharp horn
(i dill, o thill, construct til; also -dil, -thil at the end of compounds) (tine, point, sharp-pointed peak), no distinct pl. form except with article (i thill). Archaic †tild.
_ n. _horn. >> Caradhras