noun

• (uncountable) A black or brownish black rock formed from prehistoric plant remains, composed largely of carbon and burned as a fuel.
  "The coal in this region was prized by ironmasters in centuries past, who mined it in the spots where the drainage methods of the day permitted."
• (uncountable) A black or brownish black rock formed from prehistoric plant remains, composed largely of carbon and burned as a fuel.
  "Put some coal on the fire."
• (countable) A piece of coal used for burning (this use is less common in American English)
  "Put some coals on the fire."
• (countable) A glowing or charred piece of coal, wood, or other solid fuel.
  "hot coals"

verb

• (intransitive) To take on a supply of coal (usually of steam ships or locomotives).
  "1863, Colonial Secretary to Commander Baldwin, USN shortly after that she coaled again at Simon's Bay; and that after remaining in the neighbourhood of our ports for a time, she proceeded to Mauritius, where she coaled again, and then returned to this colony."
• (transitive) To supply with coal.
  "to coal a steamer"
• (intransitive) To be converted to charcoal.
  "After the initial burn the goal of any good fire should be coaling; that is, creating a bed of solid coals that will sustain the fire."
• (transitive) To burn to charcoal; to char.
  "Char-coal of roots, coaled into great pieces."