A live coal or ember.  Tolkien spelled it here as “glede”, a Middle English form of the word and also a dialectical word for a kite – a bird of prey.  Was he helping our imaginations to picture the coals and embers flying everywhere with deadly result?

• 14.024 to sparks and gledes.

“glede | gled, n.” OED Online. Oxford University Press, March 2015. Web. 20 May 2015.

“gleed, n.” OED Online. Oxford University Press, March 2015. Web. 20 May 2015.