The Collaborative International Dictionary of English v.0.48:

Filler \Fill"er\, n.
   1. One who, or that which, fills; something used for filling.
      [1913 Webster]

            'T is mere filler, to stop a vacancy in the
            hexameter.                            --Dryden.
      [1913 Webster]

            They have six diggers to four fillers, so as to keep
            the fillers always at work.           --Mortimer.
      [1913 Webster]

   2. (Paint.) A composition, as of powdered silica and oil,
      used to fill the pores and grain of wood before applying
      paint, varnish, etc.
      [Webster 1913 Suppl.]

   3. (Forestry) Any standing tree or standard higher than the
      surrounding coppice in the form of forest known as coppice
      under standards. Chiefly used in the pl.
      [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Filler \Fill"er\, n. [From 1st Fill.]
   A thill horse. [Prov. Eng.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

filler
    n 1: used for filling cracks or holes in a surface
    2: 100 filler equal 1 forint in Hungary
    3: copy to fill space between more important articles in the
       layout of a magazine or newspaper
    4: anything added to fill out a whole; "some of the items in the
       collection are mere makeweights" [syn: makeweight,
       filler]
    5: the tobacco used to form the core of a cigar