duff vs slack

duff

noun
  • Coal dust, especially that left after screening or combined with other small, unsaleable bits of coal. 

  • A mixture of coal and rock. 

  • A pudding-style dessert, especially one made with plums. 

  • The bits left in the bottom of the bag after the booty has been consumed, like crumbs. 

  • Something spurious or fake; a counterfeit, a worthless thing. 

  • An error. 

  • A stiff flour pudding, often with dried fruit, boiled in a cloth bag, or steamed. 

  • Fine and dry coal in small pieces, usually anthracite. 

  • Dough. 

  • Decaying vegetable matter on the forest floor. 

  • The buttocks. 

adj
  • Worthless; not working properly, defective. 

verb
  • To hit the ground behind the ball. 

  • To alter the branding of stolen cattle; to steal cattle. 

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. 

verb
  • To slacken. 

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

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. 

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