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!
gonn
noun. (great) stone, rock
gond
noun. stone
gonwed
adjective. rocky
gonthos
noun. great rock
The noun G. {gondos >>} gonthos “great rock” appeared in the Gnomish Lexicon, apparently a variant of G. gontha “pillar, stele, memorial” (GL/41).
Neo-Sindarin: I think the deleted Gnomish form can be adapted into Neo-Sindarin as ᴺS. gonnos, a combination of S. gond “stone” and the variant -os of the augmentative suffix S. -oth.
gondolin
place name. Stone of Song
gondothlimbar
place name. City of the Dwellers in Stone, Dwelling of the Folk of Stone
clochiol
adjective. stone
An adjective for “stone” in the Gnomish Lexicon of the 1910s appearing as an element in G. gôf·clochiol “stone-fruit” (GL/40), derived from G. cloch “a stone” (GL/26).
gontha
noun. pillar, stele, memorial
taul
noun. pillar
A word in the Gnomish Lexicon of the 1910s given as {gondriol “rock”} >> gonwen “rocky”, an adjectival form of G. gonn “great stone, rock” (GL/41).