keel petal
Botanical term for the two fused lower petals in flowers of the Fabaceae (pea) family, forming a keel-like structure.
In legume flowers, the keel petal encloses the stamens and pistil.
Compound of 竜骨 (keel, literally 'dragon bone') and 弁 (petal), describing the keel-like shape of the fused lower petals.