septum

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A thin partition or membrane that divides two cavities or soft masses of tissue in an organism: the nasal septum; the atrial septum of the heart.

Century Dictionary and Cyclopedia

1. n. A partition; a wall separating two cavities.
2. n. Specifically.
3. n. In botany, any kind of a partition, whether a proper dissepiment or not: as, the septum in a seed; the septum of a spore.
4. n. In anatomy and zoology, a partition; a wall between two cavities, or a structure which divides a part or an organ into separate portions; a dissepiment. In vertebrates the formations known as septa are most frequently situated in the vertical longitudinal median line of the body, but may be transverse or otherwise disposed. A number of them are specified by qualifying words. See phrases following.
5. n. In corals, a calcified mesentery; one of the six or more vertical plates which converge from the wall to the axis of the visceral space, dividing this into a number of radiating loculi or compartments. Each septum appears single or simple, but is really a duplicature of closely apposed plates, just as the mesentery itself is a fold. They are to be distinguished from the horizontal dissepiments, or tabulæ, which may cut them at right angles. They are variously modified in details of form, may be connected by synapticlæ, and are divided, according to their formation, into primary, secondary, and tertiary.
6. n. In conchology, one of the transverse partitions which separate the cavity of the shell of a cephalopod into chambers.
7. n. In Vermes, a sort of diaphragm, a series of which may partition a worm into several cavities.
8. n. In Protozoa, the wall between any two compartments of the test, as of a foraminifer.
9. n. Same as septum lucidum.

Wiktionary

1. n. anatomy A wall separating two cavities; a partition; as, the nasal septum.
2. n. botany A partition that separates the cells of a fruit.
3. n. zoology One of the radial calcareous plates of a coral.
4. n. zoology One of the transverse partitions dividing the shell of a mollusk, or of a rhizopod, into several chambers.
5. n. zoology One of the transverse partitions dividing the body cavity of an annelid.

GNU Webster's 1913

1. n. A wall separating two cavities; a partition.
2. n. (Bot.) A partition that separates the cells of a fruit.
3. n. One of the radial calcareous plates of a coral.
4. n. One of the transverse partitions dividing the shell of a mollusk, or of a rhizopod, into several chambers. See Illust. under Nautilus.
5. n. One of the transverse partitions dividing the body cavity of an annelid.

WordNet 3.0

1. n. (anatomy) a dividing partition between two tissues or cavities
2. n. a partition or wall especially in an ovary