The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   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.
      [1913 Webster]

            Liquids are generally heated by convection -- when
            heat is applied from below.           --Nichol.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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