ルイ
Ainu「砥」
ruymedium
Both references explicitly attest the whetstone noun. The common ruy meaning intense or strong is a separate sense and supplies no evidence for 砥.
References
Occurrences (1)
- National Institute for Japanese Language and Linguistics · 乾巻 · Page 10, line 5 · ルイ
…ヒツケ 中なるは ポイナ 小なるは ヒニケウ フリマ 砥 ルイ凝石ヲタシユマ トイシユマ軽石シユツシユツプ浜辺ピシタ浜端たシツテキシヤム ヲタシヤム川向ふベツ…