Source : Webster's Revised Unabridged Dictionary (1913)

Convection \Con*vec"tion\, n. [L. convectio, fr. convehere to
   bring together; con- + vehere to carry.]
   1. The act or process of conveying or transmitting.

   2. (Physics) A process of transfer or transmission, as of
      heat or electricity, by means of currents in liquids or
      gases, resulting from changes of temperature and other
      causes.

            Liquids are generally heated by convection -- when
            heat is applied from bellow.          --Nichol.

Source : WordNet®

convection
     n 1: the transfer of heat through a fluid (liquid or gas) caused
          by molecular motion
     2: (meteorology) the vertical movement of heat or other
        properties by massive motion within the atmosphere