(1):

(n.) The principal axis in a raceme, spike, panicle, or corymb.

(2):

(n.) The central cord in the stem of a crinoid.

(3):

(n.) The median part of the radula of a mollusk.

(4):

(n.) The continued stem or midrib of a pinnately compound leaf, as in a rose leaf or a fern.

(5):

(n.) The spine.

(6):

(n.) The shaft of a feather. The rhachis of the after-shaft, or plumule, is called the hyporhachis.

(7):

(n.) A central cord of the ovary of nematodes.