b. symmetric difference the set of members of 1 but not both of those with the supplied sets. Normally symbolized: A + Bdermal ectodermal endodermal epidermal epithermal geothermal hydrothermal intradermal isothermal mesodermal photothermal electrothermal See All Rhymes for thermal2. of, pertaining to, or of the nature of warm or heat springs: ther