Main Entry: ac·ti·nom·e·ter

Pronunciation: \ˌak-tə-ˈnä-mə-tər\

Function: noun

Date: 1833

: any of various instruments for measuring the intensity of incident radiation; especially : one in which the intensity of radiation is measured by the speed of a photochemical reaction

— ac·ti·no·me·tric \-nō-ˈme-trik\ adjective

— ac·ti·nom·e·try \-ˈnä-mə-trē\ noun