A root in The Etymologies of the 1930s glossed “abound” with derivatives such as ᴹQ. rimbe/N. rhim “crowd, host” (Ety/RIM). A likely precursor to this root appeared in the Qenya Lexicon of the 1910s as ᴱ√‘(A)ṚM(A)R and ᴱ√‘ṚMṚ with a Gnomish form ᴱ√grimri· (QL/32), indicating the actual primitive form was ✱ᴱ√ƷṚMṚ. Derivatives of this early root include ᴱQ. arm- “gather, collect” and G. grim “host, folk”, the last of these the likely precursor to N. rhim.
The root ᴹ√RIM also appeared in Primitive Quendian Structure: Final Consonants from 1936, glossed “host, large number” >> “number, plenty” (PE21/57). Quenya and Sindarin forms Q. rimbë and S. rim continued to appear in Tolkien’s later writing (Let/382; PE17/50; UT/318), so it is likely the root √RIM remained valid, especially given the prevalence of suffix -rim in Sindarin collective names.
This root first appeared in the Qenya Lexicon of the 1910s as ᴱ√RIẎI “scatter” (gloss marked with a “?” by Tolkien) with derivatives like ᴱQ. ríma “line of seeds planted, row, series, furrow”, ᴱQ. rísima “scattered, ubiquitous, universal”, and ᴱQ. rista “shoot (sowing), plant, seedling” (QL/80). Tolkien also linked it to the root ᴱ√ORO⁽⁾, which he said could be analyzed as o- (“over”) + RIẎI; that root had derivatives like ᴱQ. ore (ori-) “seed, grain” and ᴱQ. orya- “sow” (QL/70). In the Declension of Nouns from the early 1930s, Tolkien gave the root form ᴹ√RĪI̯ as the basis for ᴹQ. rí “reed, grass-stem” (PE21/38). There are no signs of this root thereafter.
Neo-Eldarin: In later writings, ᴹ√RED seems to be the basis for “scatter, sow” (PE19/91, Ety/RED), but I think it might be worth retaining the root √RIY as the basis for random scattering as opposed to intentionally scattering for purposes of planting = √RED. In theory ᴹ√RIY would conflict with ᴹ√RĪ “✱edge” (Ety/RĪ), but Tolkien revised that root to ᴹ√SRI.