coal vs slack

coal

noun
  • A piece of coal used for burning (this use is less common in American English) 

  • A type of coal, such as bituminous, anthracite, or lignite, and grades and varieties thereof, as a fuel commodity ready to buy and burn. 

  • A glowing or charred piece of coal, wood, or other solid fuel. 

  • A black or brownish black rock formed from prehistoric plant remains, composed largely of carbon and burned as a fuel. 

  • charcoal. 

verb
  • To supply with coal. 

  • To take on a supply of coal (usually of steam ships). 

  • To burn to charcoal; to char. 

  • To mark or delineate with charcoal. 

  • To be converted to charcoal. 

slack

noun
  • Small coal; coal dust. 

  • Unconditional listening attention given by client to patient. 

  • A temporary speed restriction where track maintenance or engineering work is being carried out at a particular place. 

  • A tidal marsh or shallow that periodically fills and drains. 

  • The part of anything that hangs loose, having no strain upon it. 

  • A valley, or small, shallow dell. 

adv
  • Slackly. 

adj
  • Moderately warm. 

  • Vulgar; sexually explicit, especially in dancehall music. 

  • Not active or busy, successful, or violent. 

  • Excess; surplus to requirements. 

  • Lax; not tense; not firmly extended. 

  • Lacking diligence or care; not earnest or eager. 

  • Lax. 

  • Moderate in speed. 

  • Weak; not holding fast. 

verb
  • To slacken. 

  • To lose cohesion or solidity by a chemical combination with water; to slake. 

How often have the words coal and slack occurred in a corpus of books? (source: Google Ngram Viewer )