glade (n.)

Old English glæd "bright, shining, gleaming; joyous; pleasant, gracious" (also as a noun, "joy, gladness"), from Proto-Germanic *gladaz (source also of Old Norse glaðr "smooth, bright, glad," Danish glad "glad, joyful," Old Saxon gladmod, in which the element means "glad," Old Frisian gled "smooth," Dutch glad "slippery," German glatt "smooth"), from PIE root *ghel- (2) "to shine." Apparently the notion is of being radiant with joy; the modern sense "feeling pleasure or satisfaction" is much weakened. Slang glad rags "one's best clothes" first recorded 1902.

1826, from everglade (1823), from ever, apparently in sense of "endless" + glade. Charles Vignoles's "Observations upon the Floridas" (1823) has Eternal Glades and Ever Glade morass.

The distance from the mouth of Hilsborough river to the head of the lake, in a direct line, is about 110 statute miles. The country between them is mostly, if not wholly, an everglade, by which is meant a low marsh frequently covered with water, and in which there grows a sharp triangular grass, from ten to twelve feet high, and impervious to men or animals. [American Mechanics' Magazine, Jan. 21, 1826]

"the track of moonlight on water," 1860, American English, from moon (n.) + glade (n.).