rachis

The main stem of an elongated inflorescence, as in a grass.

The main axis of a pinnately compound leaf or of a fern frond.

The main shaft of a bird’s feather, especially the part to which the barbs are attached.

The spinal column.

In botany:

The axis of an inflorescence when somewhat elongated; the continuation of the peduncle along which the flowers are ranged, as in a spike or a raceme.

In a pinnately compound leaf or frond, the prolongation of the petiole along which the leaflets or pinnæ are disposed, corresponding to the midrib of a pinnately veined simple leaf. See cut under compound.

In zoöl. and anatomy:

The vertebral column.