[W/K] :: half-duplex

  half-duplex
       
           (hdx, from telegraphy) 1. A type of
          communication channel using a single circuit which can carry
          data in either direction but not both directions at once.
       
          Compare: simplex, full-duplex.
       
          2. An obsolete term for local echo.
       
          (2001-07-21)