Source : Webster's Revised Unabridged Dictionary (1913)

Makeweight \Make"weight`\, n.
   That which is thrown into a scale to make weight; something
   of little account added to supply a deficiency or fill a gap.

Source : WordNet®

makeweight
     n 1: anything added to fill out a whole; "some of the items in
          the collection are mere makeweights" [syn: {filler}]
     2: a weight added to the scale to reach a required weight