The Collaborative International Dictionary of English v.0.48:

Fertilize \Fer"ti*lize\, v. t. [imp. & p. p. Fertilized; p.
   pr. & vb. n. Fertilizing.] [Cf. F. fertiliser.]
   1. To make fertile or enrich; to supply with nourishment for
      plants; to make fruitful or productive; as, to fertilize
      land, soil, ground, and meadows.
      [1913 Webster]

            And fertilize the field that each pretends to gain.
                                                  --Byron.
      [1913 Webster]

   2. To fecundate; as, to fertilize flower. --A. R. Wallace.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fertilize
    v 1: provide with fertilizers or add nutrients to; "We should
         fertilize soil if we want to grow healthy plants" [syn:
         fertilize, fertilise, feed]
    2: make fertile or productive; "The course fertilized her
       imagination" [syn: fertilize, fecundate, fertilise]
    3: introduce semen into (a female) [syn: inseminate,
       fecundate, fertilize, fertilise]