e·lec·tro·scope / iˈlektrəˌskōp/ • n. Physics an instrument for detecting and measuring electricity, esp. as an indication of the ionization of air by radioactivity.DERIVATIVES: e·lec·tro·scop·ic / iˌlektrəˈskäpik/ adj.

electroscope Instrument for detecting the presence of an electric charge or radiation. The commonest type is the gold-leaf electroscope, in which two gold leaves hang from a conducting rod held in an insulated container. A charge applied to the rod causes the leaves to separate, and the amount of separation indicates the amount of charge.