The Collaborative International Dictionary of English v.0.48:

Centripetal \Cen*trip"e*tal\, a. [L. centrum center + petere to
   move toward.]
   1. Tending, or causing, to approach the center.
      [1913 Webster]

   2. (Bot.)
      (a) Expanding first at the base of the inflorescence, and
          proceeding in order towards the summit.
      (b) Having the radicle turned toward the axis of the
          fruit, as some embryos.
          [1913 Webster]

   3. Progressing by changes from the exterior of a thing toward
      its center; as, the centripetal calcification of a bone.
      --R. Owen.
      [1913 Webster]

   Centripetal force (Mech.), a force whose direction is
      towards a center, as in case of a planet revolving round
      the sun, the center of the system, See Centrifugal
      force, under Centrifugal.

   Centripetal impression (Physiol.), an impression (sensory)
      transmitted by an afferent nerve from the exterior of the
      body inwards, to the central organ.
      [1913 Webster]

WordNet (r) 3.0 (2006):

centripetal
    adj 1: tending to move toward a center; "centripetal force"
           [ant: centrifugal]
    2: tending to unify [syn: centripetal, unifying(a)]
    3: of a nerve fiber or impulse originating outside and passing
       toward the central nervous system; "sensory neurons" [syn:
       centripetal, receptive, sensory(a)]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "centripetal":
   approaching, asymptotic, centrolineal, concentrating, concurrent,
   confluent, confocal, connivent, consolidating, converging, focal,
   meeting, mutually approaching, radial, radiating, tangent,
   tangential, unifying, uniting