A verb appearing as ᴹQ. rista- “cut” in The Etymologies of the 1930s under the root ᴹ√RIS “slash, rip” (Ety/RIS).
A similar set of forms “rista & risse, rinse” appeared in notes on Words, Phrases and Passages from the Lord of the Rings (WP) from the late 1950s or early 1960s derived from √RIS “cut” as part of a discussion of the etymology of S. Imladris (PE17/87). These could be various noun or adjective forms, equivalent to the final element of Imladris, but in that note Tolkien said that Sindarin element was derived from primitive ✶rinsa “cleft, cloven, separate”. Therefore, I think these Quenya forms might instead be a formative or causative verb rista- “✱to cut” with strong pasts risse or rinse.
Neo-Quenya: Given the uncertain nature of the forms from WP, I would assume rista- is (or became) an ordinary weak verb for purposes of Neo-Quenya, with a past form ✱ristane. Given the meaning of its 1930s root (“slash, rip”), I would further assume its connotation is “cut [into]” as opposed to Q. cir- “cut completely, cut apart”.
rissë noun? The word is not clearly glossed but apparently means "cut" or "cleft" (ravine), the cognate of the final element of Imladris, Sindarin name of Rivendell. (PE17:87)