A noun for “corpse” in The Etymologies of the 1930s derived from ON. ndagno under the root ᴹ√NDAK “slay” (Ety/NDAK), where the g vocalized to i before n and then ai became ae.
Conceptual Development: There were a couple of unrelated “corpse” words in Tolkien’s earlier writings. G. cweleg “corpse, dead body” appeared in the Gnomish Lexicon of the 1910s based on G. cwel- “fade, wither” (GL/28), clearly the equivalent of contemporaneous ᴱQ. qelet (qelekt-) of the same meaning (QL/76). ᴱN. rhanc “corpse, body of one slain in battle” appeared in Early Noldorin Word-lists of the 1920s related to the verb rhengi (rhang-) “to slay in battle” (PE13/152).
The Etymologies of the 1930s had N. {rhein >>} rhain “free” derived from ᴹ✶(a)ranı̯ā under the root ᴹ√RAN “wander, stray”; it also had a deleted variant erein, presumably from aranı̯ā (EtyAC/RAN). See also S. rain “erratic wandering” for a later appearance of a similarly derived word.
Neo-Sindarin: Many Neo-Sindarin writers adapt this adjective as ᴺS. rain “free” for purposes of Neo-Sindarin, as suggested in HSD (HSD), since the unvoicing of initial r to rh was a feature of Noldorin of the 1930s but not Sindarin of the 1950s and 60s. I would use it as “free” in the sense “✱unconstrained”.