The glowing embers that result when wood is burned, and that can continue to release intense heat (Ember).
1907, w, The Younger Set Chapter 3, When the flames at last began to flicker and subside, his lids fluttered, then drooped ; but he had lost all reckoning of time when he opened them again to find Miss Erroll in furs kneeling on the hearth and heaping kindling on the coals, and her pretty little Alsatian maid beside her, laying a log across the andirons.
