This root, glossed “scar, score, furrow”, appeared as part of a discussion of the origin of the Sindarin word S. ross¹ “foam” appearing in the name Elros “Star-foam” (PM/368-371). Tolkien was uncertain whether this Sindarin word could coexist with its homophone S. ross² “copper-coloured”, and investigated the possibility that Elros was instead derived from a Beorian word rôs “foam”. According to Christopher Tolkien, his father was forced to abandon this line of reasoning when he remembered that the unrelated name S. Cair Andros also contained this element, forcing it to be of Sindarin rather than Beorian origin (SD/371).

Despite all this, the related Adûnaic word Ad. roth “foam” survived in The Silmarillion in the Adûnaic name Rothinzil “Foam-flower” of Earendil’s ship. Therefore, perhaps this root remains valid. According to Tolkien, this root originally had to do with ploughs and ploughing, and was later used for the white crest of waves by analogy with the churning dirt of a furrow (PM/376).