A verb in The Etymologies of the 1930s glossed “to flow like a (?torrent)” [the last word is unclear] under the root ᴹ√RIP “rush, fly, fling” (Ety/RIP). It was related to the name N. Rhibdath or Rhimdath “Rushdown”. It had a past form rhimp followed by another form rhimmo, possibly a Noldorin-style infinitive of a longer variant ✱rhimma-.
Neo-Sindarin: Most Neo-Sindarin writers adapt this Noldorin word as ᴺS. rib- “arm” 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.
The reading of the gloss is uncertain