bilat?eral sym?metry n. a basic body plan in which the left and right sides of the organism can be divided into approximate mirror images of each other. Compare radial symmetry. [1850?55] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.zygomorphismthe state or quality of being bilaterally symmetrical, as certain organisms. ? zygomorphic, zygomorphous, adj.See also: Organismsthe state or quality of being bilaterally symmetrical, as certain organisms. Cf. monosymmetry. ? zygomorphic, zygomorphous, adj.See also: Biology-Ologies & -Isms. Copyright 2008 The Gale Group, Inc. All rights reserved.