The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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