1. (n.) An axis to which a carpel of a compound pistil may be attached, as in the case of the geranium; or which is left when a pod opens.

2. (n.) A column like axis in the capsules of mosses.

3. (n.) A term applied to various column like parts; as, the columella, or epipterygoid bone, in the skull of many lizards; the columella of the ear, the bony or cartilaginous rod connecting the tympanic membrane with the internal ear.

4. (n.) The upright pillar in the axis of most univalve shells.

5. (n.) The central pillar or axis of the calicles of certain corals.