Source : Webster's Revised Unabridged Dictionary (1913)

Transpiration \Tran`spi*ra"tion\, n. [F. transpiration.]
   1. (Physiol.) The act or process of transpiring or excreting
      in the form of vapor; exhalation, as through the skin or
      other membranes of the body; as, pulmonary transpiration,
      or the excretion of aqueous vapor from the lungs.
      Perspiration is a form of transpiration. --Cudworth.

   2. (bot.) The evaporation of water, or exhalation of aqueous
      vapor, from cells and masses of tissue.

   3. (Physics) The passing of gases through fine tubes, porous
      substances, or the like; as, transpiration through
      membranes.

Source : WordNet®

transpiration
     n 1: the passage of gases through fine tubes because of
          differences in pressure or temperature
     2: the process of givng off or exhaling water vapor through the
        skin or mucous membranes
     3: the emission of water vapor from the leaves of plants