The Collaborative International Dictionary of English v.0.48:

Fossilize \Fos"sil*ize\, v. t. [imp. & p. p. Fossilized; p.
   pr. & vb. n. Fossilizing.] [Cf. F. fossiliser.]
   1. To convert into a fossil; to petrify; as, to fossilize
      bones or wood.
      [1913 Webster]

   2. To cause to become antiquated, rigid, or fixed, as by
      fossilization; to mummify; to deaden.
      [1913 Webster]

            Ten layers of birthdays on a woman's head
            Are apt to fossilize her girlish mirth. --Mrs.
                                                  Browning.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Fossilize \Fos"sil*ize\, v. i.
   1. To become fossil.
      [1913 Webster]

   2. To become antiquated, rigid, or fixed, beyond the
      influence of change or progress.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fossilize
    v 1: convert to a fossil; "The little animals fossilized and are
         now embedded in the limestone" [syn: fossilize,
         fossilise]
    2: become mentally inflexible [syn: fossilize, fossilise]