What does the word duplex mean?

Usage examples for duplex

  1. April 23, 1873 162, 633 Duplex Telegraphs. – Edison, His Life and Inventions by Frank Lewis Dyer and Thomas Commerford Martin
  2. On viewing together the system of vessels proper to each heart, they will be seen to exhibit in respect to the body a figure in doubly symmetrical arrangement, of which the united hearts form a duplex centre. – Surgical Anatomy by Joseph Maclise