retto "climber" (PE17:182, language unidentified). The form is mentioned as somehow related to the Sindarin element -reth in Orodreth ("Mountain-climber") and could be either Old Sindarin or the Quenya cognate. *Ret- might then be the Quenya verb for "climb", a derivative of the root RETE of similar meaning.
Quenya
retto
noun. *climber
retto
climber
An apparently Quenya word in 1957 Notes on Names (NN), based on the root √RET and equivalent to S. reth, the latter an element in the name S. Orodreth “Mountaineer” (PE17/182). It is thus likely that Q. retto and S. reth means something like “✱climber”, though it is possible that retto is actually a primitive form.