Definition of "dingle"

Turning to the left and skirting this huge hedge Treebeard came in a few strides to a narrow entrance. Through it a worn path passed and dived suddenly down a long steep slope. The hobbits saw that they were descending into a great dingle, almost as round as a bowl, very wide and deep, crowned at the rim with the high dark evergreen hedge.

1954, J. R. R. Tolkien, “Chapter 4”, in The Two Towers, Book III