A root appearing Notes on Names (NN) from 1957 serving as an explanation for the element S. thorn “steadfast” in the name S. Arathorn, first appearing in a rejected page with variants √STOR and √THOR (PE17/113-114) and then later as only √THOR (PE17/113). This root may be connected to Q. torna “hard” in notes on Quenya intensive forms written between the first and second edition of The Lord of the Rings, where it was an element in Q. tornanga “hard iron”, with intensive forms aristorna, anastorna that imply derivation from √STOR (PE17/56).
Neo-Eldarin: For purposes of Neo-Eldarin, I would assume this root is √STOR to avoid conflict with ᴹ√THOR(ON), the basis for “eagle” words.
A root glossed “strip, flay, peel off” in notes on The Rivers and Beacon-hills of Gondor from 1967-69 given to explain the second element of S. Calenhad as S. sâdh, with Tolkien stating that “dh” is generally represented as “d” in his maps (VT42/20). The root is mentioned nowhere else.