: a projection suggesting the keel of a boat or ship: such as
a
: an anatomical process forming a ridge (as on the sternum of a bird) : carinasense 1
b
botany: the lower part of a papilionaceous flower (as of a pea or bean plant) that consists of two fused petals, lies between the wings (see wingsense 2e(2)), and encloses the pistil and stamens
The keel, the lowest petal of the pea-like flower, is short and rounded. Sylvan T. Runkel and Dean M. Roose