龙骨 is a compound word (dragon + bone) that covers multiple technical and anatomical concepts across different fields. In everyday use it refers to the backbone or spine; in nautical and aeronautical contexts it means the keel of a ship or hull of an aircraft; and in traditional Chinese medicine it denotes fossilized animal bones (usually from ancient mammals) used as a mineral remedy. The botanical sense (keel petal) is limited to specialist botany texts.