Doriathrin
thall
adjective. steep, falling steeply (of river)
Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!
An adjective appearing as Ilk. thall “steep, falling steeply (of river)” in The Etymologies of the 1930s, derived from primitive ᴹ✶stalrā and an element in thalos “torrent” (Ety/STAL). The [[ilk|initial [s] spirantalized the following [t] to [θ] (“th”)]], and the [[mp|[lr] became [ll]]], as suggested by Helge Fauskanger (AL-Ilkorin/thall). Since the name Thalos survived in Tolkien’s later writings, presumably thall “steep, falling steeply” became Sindarin after Ilkorin was abandoned.