1.  rachis(n = noun.plant) Array - axis of a compound leaf or compound inflorescence; Array
is a kind of axis

2.  rachis(n = noun.body) back, backbone, spinal column, spine, vertebral column - the series of vertebrae forming the axis of the skeleton and protecting the spinal cord; "the fall broke his back"
is a kind of skeletal structure
is a part of axial skeleton
has parts: canalis vertebralis, spinal canal, vertebral canal, coccyx, tail bone, vertebra, intervertebral disc, intervertebral disk
has particulars: notochord, chine

1.  The spine; the vertebral column. [1913 Webster]

2.  Same as Rhachis. [1913 Webster]

rachis, n. (pl. rachides)
1 Bot. a a stem of grass etc. bearing flower-stalks at short intervals. b the axis of a compound leaf or frond.
2 Anat. the vertebral column or the cord from which it develops.
3 Zool. a feather-shaft, esp. the part bearing the barbs.

Derivative:
rachidial adj.

Etymology:
mod.L f. Gk rhakhis spine: the E pl. -ides is erron.