The earliest appearance of this root was ᴹ√TOTO- “repeat” from Demonstrative, Relative, and Correlative Stems (DRC) from 1948 (PE23/109). The root appeared as √TŌ/OTO in a discussion of prefixes for “back” from around 1959, where Tolkien specified its meaning as “back as an answer, or return by another agent to an action affecting him, as in answering, replying, avenging, requiting, repaying, rewarding”; Tolkien also considered the forms √UTU/TŪ (PE17/166). In this 1959 note Tolkien crossed √TŌ/OTO through and seems to have replaced it with √KHAN. Tolkien mentioned the root √OT in a discussion of numbers from the late 1960s, but only to specify that “there was no primitive base OT-” (VT47/16).
Primitive elvish
(n)dan
root. back (again); retreat, go back, give way (as one advances), revert, back (again), [ᴹ√] backwards; [√] retreat, go back, give way (as one advances), revert, [ᴹ√] return
khan
root. back
tō/oto
root. back
The most notable use of the root √(N)DAN “back(wards)” was in the name Q. Nandor for those Elves who joined in the march to Valinor but turned back during the journey (VT48/32); the same root was an element in the earlier name for the Nandor from the 1930s, the Danas (Ety/NDAN). The root first appeared as ᴹ√NDAN “back” in The Etymologies of the 1930s with derivatives like the aforementioned Danas as well as the prefix ᴹQ. nan- “backwards” and the Doriathrin noun dôn “back” (Ety/NDAN). The Etymologies also mentioned an unstrengthened form of the root ᴹ√DAN (Ety/DAN).
The root √(N)DAN appeared several times in Tolkien’s later writings. It appeared among a list of roots having to do with “back” probably composed around 1959 (PE17/166). In this list, Tolkien clarified that in Quenya, √NDAN specifically meant “back” as an action by the same agent revising a previous action, as opposed to an action by a different agent, for which Tolkien coined the root {√TŌ/OTO >>} √KHAN; the example Tolkien gave was Q. nanwen-/S. dadwen- “return, go back [by same agent]” < √NDAN vs. {{Q. tóquet- >>} Q. hanquenta “answer [by a different agent]”. This distinction was lost in Sindarin, however, and √NDAN came to be used for both same and differing agents. Tolkien also said that √NDAN could be used “of return (in same path), retracing, and so employable as un- as in undo”.
The root was mentioned again in the Quendi and Eldar essay from 1959-60, where Tolkien said:
> The name Nandor was a derivative of the element ✱dan, ✱ndan- indicating the reversal of an action, so as to undo or nullify its effect, as in “undo, go back (the same way), unsay, give back (the same gift: not another in return)”. The original word ✱ndandō, therefore, probably only implied “one who goes back on his word or decision”.
Finally, the root appeared in some notes from the late 1960s where √dan- was glossed “retreat, go back, give way (as one advances), revert” serving as the basis for {✶danmi >>} ✶ndanmē > Q. nanwë/S. dannen “ebb-tide”, apparently originally meaning “retreat” (VT48/26 author’s note #2, VT48/32 editor’s note #18). In the same document Tolkien again mentioned the connection of this root to the name of the Nandor.