Definition of "keel"

noun:
- A large beam along the underside of a ship's hull from bow to stern.
  
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- Sometimes, a rigid, flat piece of material anchored to the lowest part of the hull of a ship to give it greater control and stability.
  
  from Wiktionary, Creative Commons Attribution/Share-Alike License
- A type of flat-bottomed boat.
  
  from Wiktionary, Creative Commons Attribution/Share-Alike License
- Something similar to chalk or crayon used to mark pavement.
  
  from Wiktionary, Creative Commons Attribution/Share-Alike License
verb:
- To collapse, to fall.
  
  from Wiktionary, Creative Commons Attribution/Share-Alike License