Merriam-Webster Collegiate Dictionary - symmetrical

 or symmetric  adjective  Date: 1653  1. having, involving, or exhibiting symmetry  2. having corresponding points whose connecting lines are bisected by a given point or perpendicularly bisected by a given line or plane ~ curves  3. (symmetric) being such that the terms or variables may be interchanged without altering the value, character, or truth symmetric equations R is a symmetric relation if aRb implies bRa  4.  a. capable of division by a longitudinal plane into similar halves ~ plant parts  b. having the same number of members in each whorl of floral leaves ~ flowers  5. affecting corresponding parts simultaneously and similarly ~ rash  6. exhibiting symmetry in a structural formula; especially being a derivative with groups substituted ~ly in the molecule  • ~ly adverb  • ~ness noun