The Collaborative International Dictionary of English v.0.48:

Registration \Reg`is*tra"tion\ (-tr?"sh?n), n. [LL. registratio,
   or F. r['e]gistration. See Register, v.]
   1. The act of registering; registry; enrollment.
      [1913 Webster]

   2. (Mus.) The art of selecting and combining the stops or
      registers of an organ.
      [1913 Webster]

WordNet (r) 3.0 (2006):

registration
    n 1: the act of enrolling [syn: registration, enrollment,
         enrolment]
    2: the body of people (such as students) who register or enroll
       at the same time [syn: registration, enrollment]
    3: a document certifying an act of registering
    4: (music) the sound property resulting from a combination of
       organ stops used to perform a particular piece of music; the
       technique of selecting and adjusting organ stops
    5: the act of adjusting something to match a standard [syn:
       adjustment, registration, readjustment]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "registration":
   booking, cataloging, chronicling, enlistment, enrollment, entering,
   entry, filing, impanelment, indexing, inscribing, inscription,
   insertion, inventorying, itemization, listing, logging,
   matriculation, posting, record keeping, recordation, recording,
   register, registry, tabulation