The Collaborative International Dictionary of English v.0.48:

completing \completing\ adj.
   serving to complete.

   Syn: complemental, complementary, supplemental,
        supplementary.
        [WordNet 1.5 +PJC]

The Collaborative International Dictionary of English v.0.48:

Complete \Com*plete"\, v. t. [imp. & p. p. Completed; p. pr. &
   vb. n. Completing.]
   To bring to a state in which there is no deficiency; to
   perfect; to consummate; to accomplish; to fulfill; to finish;
   as, to complete a task, or a poem; to complete a course of
   education.
   [1913 Webster]

         Bred only and completed to the taste
         Of lustful appetence.                    --Milton.
   [1913 Webster]

         And, to complete her bliss, a fool for mate. --Pope.

   Syn: To perform; execute; terminate; conclude; finish; end;
        fill up; achieve; realize; effect; consummate;
        accomplish; effectuate; fulfill; bring to pass.
        [1913 Webster]

WordNet (r) 3.0 (2006):

completing
    adj 1: acting as or providing a complement (something that
           completes the whole) [syn: complemental,
           complementary, completing]