Source : WordNet®

simplex
     adj 1: allowing communication in only one direction at a time, or
            in telegraphy allowing only one message over a line at
            a time; "simplex system"
     2: having only one part or element; "a simplex word has no
        affixes and is not part of a compound--like `boy' compared
        with `boyish' or `house' compared with `houseboat'"

Source : Free On-Line Dictionary of Computing

simplex
     
        1.  Used to describe a communications channel
        that can only ever carry a signal in one direction, like a
        one-way street.  Television is an example of ({broadcast})
        simplex communication.
     
        Opposite: {duplex}.
     
        2.  The {simplex method}.
     
        (2001-07-21)