A verb appearing in its Noldorin-style infinitive form N. rhisto in The Etymologies of the 1930s as a cognate to ᴹQ. rista- “cut”, both derived from the root ᴹ√RIS (Ety/RIS). In the initial version of this root’s entry it appeared as risto derived from ON. rista- “rend, rip” (Ety/RIS). The original entry was not deleted, and it is not clear if its retention was an oversight or if Tolkien intended both meanings to coexist.
Neo-Sindarin: In Noldorin, an initial r unvoiced to rh, but this was not the case in Sindarin, so its Sindarin form is probably ᴺS. rista-, as suggested in HSD (HSD). I would further assume rista- can mean any of “cut, rend, rip”.
This form replaced deleted goloth in the manuscript of The Etymologies, see VT/45:29. The deleted form is however also later attested in VT/42:18