The Collaborative International Dictionary of English v.0.48:

Christen \Chris"ten\, v. t. [imp. & p. p. Christened; p. pr. &
   vb. n. Christening.] [AS. cristnian to make a Christian,
   fr. cristen a Christian.]
   [1913 Webster]
   1. To baptize and give a Christian name to.
      [1913 Webster]

   2. To give a name; to denominate. "Christen the thing what
      you will." --Bp. Burnet.
      [1913 Webster]

   3. To Christianize. [Obs.] --Jer. Taylor.
      [1913 Webster]

   4. To use for the first time. [Colloq.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

christen
    v 1: administer baptism to; "The parents had the child baptized"
         [syn: baptize, baptise, christen]