noun

• (nautical) A large beam along the underside of a ship’s hull from bow to stern.
  "I hear the noise about thy keel; ⁠I hear the bell struck in the night: ⁠I see the cabin-window bright; I see the sailor at the wheel."
• (nautical) A rigid, flat piece of material anchored to the lowest part of the hull of a ship to give it greater control and stability.
• (aeronautics) In a dirigible, a construction similar in form and use to a ship's keel; in an aeroplane, a fin or fixed surface employed to increase stability and to hold the machine to its course.
• (by extension) The rigid bottom part of something else, especially an iceberg.
  "The most important ice features are the frequency and extent of downward projections (bummocks and ice keels) from the underside of the ice canopy (pack ice and enclosed water areas from the point of view of the submariner)[…]"

verb

• (intransitive, followed by "over") to collapse, to fall
  "He keeled over after having a stroke."

verb

• (transitive, obsolete) To cool; make cool; to cool by stirring or skimming in order to keep from boiling over.
  "while greasy Joan doth keel the pot (Shakespeare)"
• (transitive, obsolete) To moderate the ardour or intensity of; assuage; to appease, pacify, or lessen.
• (intransitive, obsolete) To become cool; cool down.

noun

• (brewing) A broad, flat vessel used for cooling liquids; a brewer's cooling vat; a keelfat.