I. fōˈtäməd.ə(r) noun
Etymology: New Latin photometrum, from phot- + -metrum -meter
: an instrument for measuring luminous intensity, luminous flux, illumination, or brightness by comparison of two unequal lights from different sources usually by reducing the illumination of one (as by varying the distance of the source or using a polarizing device) until the two lights appear equal, the amount of adjustment serving as the basis of comparison and the equality of illumination being judged by various means
II. transitive verb
: to examine with a photometer