keel

1. (nautical) A large beam along the underside of a ship’s hull from bow to stern.Examples: "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."

2. (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.

3. (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.

4. (by extension) The rigid bottom part of something else, especially an iceberg.Examples: "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)[…]"; "Bill Roggensack, EBA Engineering Ltd.: So at the end of this particular simulation, presumably the keel of the iceberg is in contact with the seabed? / Chris Woodworth-Lynas: It is just in contact with the seabed."; "Would he be able to break through the surface ice or would they ram into an ice keel extending down from the bottom of the ice pack that would rip their craft open like a mere sardine can?"broadly

5. (nautical) A type of flat-bottomed boat.Examples: "The ladies remained at the house, while the men walked to the staith on the [River] Wear, and were shown the process of unloading the wagons into the keels by means of the coal-drop."

6. (zoology) The periphery of a whorl extended to form a more or less flattened plate; a prominent spiral ridge.Examples: "Metanotum shining, indistinctly punctured at the base in the centre, the sides closely punctured; the areola large, obliquely narrowed at the base, its apex open, there are 2 lateral areas, both widely open at the base on the outerside; the posterior median area bears about 10 stout, transverse keels; on its apical outerside is a triangular area; the spiracular is bounded on the outerside by a distinct keel."