What is the meaning of the word "simplex"?

Definitions:

  1. allowing communication in only one direction at a time, or in telegraphy allowing only one message over a line at a time copy to clipboard adjective
    • simplex system copy to clipboard
  2. having only one part or element copy to clipboard adjective
    • a simplex word has no affixes and is not part of a compoundlike `boy' compared with `boyish' or `house' compared with `houseboat' copy to clipboard