Merriam-Webster Collegiate Dictionary - invocation

 noun  Etymology: Middle English invocacioun, from Middle French & Latin; Middle French ~, from Latin ~-, invocatio, from invocare  Date: 14th century  1.  a. the act or process of petitioning for help or support; specifically often capitalized a prayer of entreaty (as at the beginning of a service of worship)  b. a calling upon for authority or justification  2. a formula for conjuring ; incantation  3. an act of legal or moral implementation ; enforcement  • ~al adjective  • invocatory adjective