Fluorescence (flo͝orĕs`əns), luminescence in which light of a visible color is emitted from a substance under stimulation or excitation by light or other forms of electromagnetic radiation or by certain other means. The light is given off only while the stimulation continues;
watch and ward noun Definition of WATCH AND WARD 1 : continuous unbroken vigilance and guard 2 : service as a watchman or sentinel required from a feudal tenant