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]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "christen":
   anoint, asperge, asperse, baptize, bring up, broach, call, define,
   denominate, designate, dip, dub, entitle, establish, float, found,
   identify, immerse, inaugurate, induct, initiate, install,
   institute, introduce, label, launch, lift up, name, nickname,
   nominate, raise, ring in, set agoing, set on foot, set up, specify,
   sprinkle, start going, start up, style, tag, term, title, turn on,
   usher in