Easton's Bible Dictionary
It is by no means certain that the Hebrews were acquainted with mineral coal, although it is found in Syria. Their common fuel was dried dung of animals and wood charcoal. Two different words are found in Hebrew to denote coal, both occurring in Proverbs 26:21, "As coal [Hebrews peham; i.e., "black coal"] is to burning coal [Hebrews gehalim]." The latter of these words is used in Job 41:21; Proverbs 6:28; Isaiah 44:19. The words "live coal" in Isaiah 6:6 are more correctly "glowing stone." In Lamentations 4:8 the expression "blacker than a coal" is literally rendered in the margin of the Revised Version "darker than blackness." "Coals of fire" (2 Samuel 22:9, 13; Psalm 18:8, 12, 13, etc.) is an expression used metaphorically for lightnings proceeding from God. A false tongue is compared to "coals of juniper" (Psalm 120:4; James 3:6). "Heaping coals of fire on the head" symbolizes overcoming evil with good. The words of Paul (Romans 12:20) are equivalent to saying, "By charity and kindness thou shalt soften down his enmity as surely as heaping coals on the fire fuses the metal in the crucible."
Noah Webster's New International Dictionary of the English Language
1. (n.) A thoroughly charred, and extinguished or still ignited, fragment from wood or other combustible substance; charcoal.
2. (n.) A black, or brownish black, solid, combustible substance, dug from beds or veins in the earth to be used for fuel, and consisting, like charcoal, mainly of carbon, but more compact, and often affording, when heated, a large amount of volatile matter.
3. (v. t.) To burn to charcoal; to char.
4. (v. t.) To mark or delineate with charcoal.
5. (v. t.) To supply with coal; as, to coal a steamer.
6. (v. i.) To take in coal; as, the steamer coaled at Southampton.