A receiver of a telephone to hold near to one's ear.
The arm on a pair of glasses that hooks over the ear to hold them in place.
A speaker placed inside or held near to the ear.
An electronic device that generates and amplifies a carrier wave, modulates it with a meaningful signal derived from speech, music, TV or other sources, and broadcasts the resulting signal from an antenna.
One who or that which transmits something (in all senses).