A hypothetical Sindarin name for Gondolin if it had developed from the same primitive form as its Quenya name Ondolindë (PE17/133), also appearing as Goen(g)lin (PE17/29).
Sindarin
gondolin
place name. Hidden Rock, (originally) Singing Stone
gon(g)lin Reconstructed
place name. Singing Stone, Stone of Music
The hidden city of the Noldor in Beleriand, translated “Hidden Rock”, an adaptation of its Quenya name Ondolindë “Rock of the Music of Water” (S/125). Tolkien stated that the name Gondolin was properly “neither Sindarin or Noldorin [Quenya]” (PE17/29), but the Sindarized name was reinterpretated as a combination of gond “stone” and dolen “hidden” (WJ/201).
Conceptual Development: The name G. Gondolin appeared in the earliest Lost Tales, but at this stage it was translated “Stone of Song” (LT2/158). This was the same meaning as its early Qenya name Ondolinda, with the second element being G. dólin “song” (GL/29, 41; LT1A/Gondolin). In The Etymologies from the 1930s, Tolkien revised the meaning of N. Gondolin to “heart of hidden rock” (Ety/DUL), setting the stage for the later derivation described above.