Keel/kiːl/ Definition 1 of 4Pro Tip 1/3Ship Stability The keel provides stability to a ship, so it's fundamental in nautical architecture. Shipbuilders ensure the keel is straight for optimal balance. Pro Tip 2/3Construction Phrase 'Lay the keel' refers to the start of ship construction, similar to laying a foundation. The shipyard will lay the keel for the new vessel next week. Pro Tip 3/3Nautical Term 'Keel' is a technical term; use it when discussing ships or boat construction. The old fishing boat had barnacles attached to its keel.