A verb in The Etymologies of the 1930s glossed “to rend” derived from the root ᴹ√NARAK “tear, rend (tr. and intr.)” (Ety/NÁRAK; EtyAC/NÁRAK). In The Etymologies as published in The Lost Road Christopher Tolkien gave the form as narki (LR/375), but Carl Hostetter and Patrick Wynne corrected this to narka in their Addenda and Corrigenda to the Etymologies (VT45/37).
Qenya
askat-
verb. to rend, break asunder
sakkat-
verb. to rend, break asunder
narka-
verb. to rend
The verb ᴹQ. terhat- “break apart” appeared in The Etymologies of the 1930s, a combination of ᴹQ. ter “through” with the root ᴹ√SKAT “break asunder” (Ety/SKAT). Its past form terhante “broke” appeared in earlier versions of the Lament of Atalante from the 1930s (LR/47, 56). In versions of the poem associated with The Notion Club Papers from the 1940s, Tolkien revised terhante to askante “sunder-broke” (SD/310), and in the final version of the poem he had sakkante “rent” (SD/246). The past form sakkante is difficult to puzzle out, but askante is probably based on an augmented form askat- of the root ᴹ√SKAT.
Neo-Quenya: For purposes of Neo-Quenya, I would retain both terhat- “to break apart” and askat- “to rend, break asunder” as near synonyms, both more distinctive than the basic verb ᴹQ. hat- “break asunder”.