A root in a discussion of prefixes for “back” from around 1959, which Tolkien specified as meaning: “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). But Tolkien crossed this all 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
rad
root. *back, return, [ᴹ√] back, return
aklar(a)
noun. radiance, brilliance, glory
gillingalati
masculine name. radiant stars, Gil-galad
gaili
noun. ray
ak(a)lar
noun. *radiance
kalat
noun. light
khan
root. back
tō/oto
root. back
áse
noun. sunlight
(s)rō Reconstructed
root. east
This root first appeared in The Etymologies of the 1930s as ᴹ√RAD “back, return” with derivatives like ᴹQ. randa/N. anrand “cycle, age (100 Valian Years)” as well as Dor. radhon “east” (Ety/RAD). It reappeared (unglossed) in Outline of Phonology (OP2) as an example of a root where medial d dissimilated to l in Quenya rather than becoming r as usual: √RAD > Q. ral- (PE19/99). Neither the root or the verb were glossed in OP2, so it is unclear whether or not it retained its 1930s meaning, though there is no reason to believe it didn’t.