Derndingle
From Tolkien Gateway
Derndingle was a hollow in the south of Fangorn Forest, used by the Ents from time immemorial as the place where they met in Entmoot. In shape it was a wide round depression, surrounded by a dark green hedge of evergreen trees. The hollow itself was clear of trees, except for three tall silver birches that grew in its centre.
Etymology
The name Derndingle is Mannish in origin but of course comes from an old version Westron when Gondorians still remembered the Ents.[1]
A dingle is a 'tree-shadowed dell'. The archaic element dern (also seen in Dernhelm) means 'secret, hidden'