Source : Webster's Revised Unabridged Dictionary (1913)

Fertilizer \Fer"ti*lizer\, n.
   1. One who fertilizes; the agent that carries the fertilizing
      principle, as a moth to an orchid. --A. R. Wallace.

   2. That which renders fertile; a general name for commercial
      manures, as guano, phosphate of lime, etc.

Source : WordNet®

fertilizer
     n : any substance such as manure or a mixture of nitrates used
         to make soil more fertile [syn: {fertiliser}, {plant food}]