1. (n.) The spine.

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

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

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

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

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

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