The Collaborative International Dictionary of English v.0.48:

Back \Back\, a.
   1. Being at the back or in the rear; distant; remote; as, the
      back door; back settlements.
      [1913 Webster]

   2. Being in arrear; overdue; as, back rent.
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   3. Moving or operating backward; as, back action.
      [1913 Webster]

   Back blocks, Australian pastoral country which is remote
      from the seacoast or from a river. [Webster 1913 Suppl.]


   Back charges, charges brought forward after an account has
      been made up.

   Back filling (Arch.), the mass of materials used in filling
      up the space between two walls, or between the inner and
      outer faces of a wall, or upon the haunches of an arch or
      vault.

   Back pressure. (Steam Engine) See under Pressure.

   Back rest, a guide attached to the slide rest of a lathe,
      and placed in contact with the work, to steady it in
      turning.

   Back slang, a kind of slang in which every word is written
      or pronounced backwards; as, nam for man.

   Back stairs, stairs in the back part of a house; private
      stairs. Also used adjectively. See Back stairs,
      Backstairs, and Backstair, in the Vocabulary.

   Back step (Mil.), the retrograde movement of a man or body
      of men, without changing front.

   Back stream, a current running against the main current of
      a stream; an eddy.

   To take the back track, to retrace one's steps; to retreat.
      [Colloq.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Filling \Fill"ing\, n.
   1. That which is used to fill a cavity or any empty space, or
      to supply a deficiency; as, filling for a cavity in a
      tooth, a depression in a roadbed, the space between
      exterior and interior walls of masonry, the pores of
      open-grained wood, the space between the outer and inner
      planks of a vessel, etc.
      [1913 Webster]

   2. The woof in woven fabrics.
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   3. (Brewing) Prepared wort added to ale to cleanse it.
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   Back filling. (Arch.) See under Back, a.
      [1913 Webster]