Bilateral symmetry has to do with the property of symmetry about a vertical plane. Biologists also use the term to refer to an organism which one can divide into mirrored halves like humans, frogs and cats. (Starfish, bacteria, and jellyfish possess other multiple symmetries.)
For lack of a better term, I use bilateral symmetry to refer to two word meanings that do not possess semantic symmetry. For example, "Believing" and "accepting" do not necessarily mean the same thing. Belief may require acceptance, but acceptance does not require belief.