molecularity
number of reactant molecular entities that are involved in the 'microscopic chemical event' constituting an elementary reaction
en-US/moʊˌlɛkjəˈlæɹɪti/
en-GB/məlɛkjʊlæɹɪtiː/
number of reactant molecular entities that are involved in the 'microscopic chemical event' constituting an elementary reaction