From WordNet (r) 1.6 [wn]:

  transmission
       n 1: the act of sending a message; causing a message to be
            transmitted [syn: {transmittal}, {transmitting}]
       2: communication by means of transmitted signals
       3: the fraction of radiant energy that passes through a
          substance [syn: {transmittance}]
       4: an incident is which an infectious disease is transmitted
          [syn: {infection}, {contagion}]
       5: the gears that transmit power from an automobile engine via
          the driveshaft to the live axle