earphone: electro-acoustic transducer for converting electric signals into sounds; it is held over or inserted into the ear
electro-acoustic transducer: a transducer that converts electrical to acoustic energy or vice versa
boric acid: a white or colorless slightly acid solid that is soluble in water and ethanol; used in the manufacture of glass and paper and adhesives and in detergents and as a flux in welding; also used as an antiseptic and food preservative