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
ret-
verb. to climb
retto
climber
A neologism for “to climb” coined by Helge Fauskanger for his NQNT (NQNT) based on the root √RET of the same meaning.