sept-, septi-, septo-

(Latin: a partition; a dividing wall between two spaces, tissues, or cavities; from saepire "to enclose, to hedge in", and from saepes, "fence, hedge")

septum (s) (noun), septa (pl)
A partition or a dividing wall between two spaces or cavities: "The septum is a medical term for a thin separation within, or between, certain parts of the body; for example, the nasal septum is the sheet of cartilage and bone that separates the nostrils of the nose."
transparent septum, septum pellucidum (s) (noun); transparent septa, septa pellucida (pl)
A thin plate of brain tissue, containing nerve cells and fibers, that is stretched like a flat, vertical sheet between the column and body of fornix (arched bundle of fibers); a triangular double membrane situated in the median plane and separating the anterior horns of the lateral ventricles of the brain.