This root first appeared as ᴹ√RAT “walk” in The Etymologies of the 1930s with derivatives like N. râd “path, track”, N. ostrad “street”, N. rath “course, river-bed”, and N. rant “lode, vein”, the last with the meaning Ilk. rant “flow, course of river” in Ilkorin (Ety/RAT). Hints of this root can be seen as early as the Gnomish Lexicon of the 1910s in words like G. rada “track, path, way” with primitive form rad·, probably actually ✱ᴱ√RATA (GL/64).
ᴹ√RATA reappeared on a rejected page of roots in the Quenya Verbal System from the 1940s with the gloss “go in a line (as a road)” (PE22/127). Above it Tolkien wrote “usually of animals/or two feet is {SRATA}”, perhaps indicating Tolkien was divorcing this root from the sense “walk”, which in later writings seems to be attributed to the root ✱√PAT (PE17/34).
In notes from the late 1960s Tolkien glossed √RAT as “find a way”, saying it “applied to persons journeying in the wild; to travel in roadless land; and also to streams and rivers and their courses” (NM/363). In this document it was the basis for S. rant “course” in S. Celebrant “Silverlode”, as well as Q. ratta “track” and S. rath “(climbing) street”, the latter also influenced by √RATH “climb” that was itself a more emphatic variant of √RAT (NM/354).
The extended root √ARAT “good, excellent, noble” appeared in 1957 Quenya Notes (QN) as an extension of √AR “beyond, further than”, and was principally used for the adjectives Q. ar(a)ta, S. arod/raud “noble” and elaborations thereof (PE17/147). In Definitive Linguistic Notes (DLN) from 1959 it was instead given as √RAT “tower up”, serving as the basis for the same set of words (PE17/186). In any case, all these seem to be variants of √RĀ/ARA “noble”; see that entry for details.