Webster's English Dictionary

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transpiration

tran.spi.ra.tion \.tran(t)s-p*-'ra--sh*n\ n : an act or instance of 
   transpiring : as  : the passage of fluid through an animal membrane in the 
   form of a vapor;  also : material so transpired : the emission of watery 
   vapor from the surface of plant parts (as leaves )