• (n.) One side of an echinoderm, including a pair of ambulacra, in distinction from the opposite side (trivium), which includes three ambulacra.
Biv'i·um noun [ Latin , a place with two ways. See Bivious .] (Zoology) One side of an echinoderm, including a pair of ambulacra, in distinction from the opposite side ( trivium ), which includes three ambulacra.