The Collaborative International Dictionary of English v.0.48:

Offset \Off*set"\, v. t. [imp. & p. p. Offset; p. pr. & vb. n.
   Offsetting.]
   1. To set off; to place over against; to balance; as, to
      offset one account or charge against another.
      [1913 Webster]

   2. To form an offset in, as in a wall, rod, pipe, etc.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

offsetting \off`set"ting\ adj.
   Compensating for.

   Syn: countervailing, compensatory, compensative.
        [WordNet 1.5]

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "offsetting":
   amendatory, amends, annulling, annulment, antacid, atonement,
   balancing, buffering, canceling, cancellation, commutation,
   compensating, compensation, compensatory, counteracting,
   counteraction, counteractive, counterbalancing, countervailing,
   expiation, expiatory, frustration, indemnification,
   indemnificatory, indemnity, invalidation, lex talionis, negating,
   neutralization, neutralizing, nullification, nullifying,
   penitential, recompense, recompensive, rectification, rectifying,
   redress, reparation, reparative, repayment, restitution,
   retaliation, retaliatory, revenge, satisfaction, stultifying,
   substitution, thwarting, undoing, vitiating, vitiation, voiding