modulator-demodulator
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mod´u`la`tor-de`mod´u`la`tor
n. 1. An electronic device that converts electronic signals into sound waves, and sound waves into electronic signals, used to transmit information between computers by the use of ordinary telephone lines; usually called a modem.
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.