Back filling at English => English (Websters 1913) Of Explained:
Back \Back\, a.
1. Being at the back or in the rear; distant; remote; as, the
back door; back settlements.
2. Being in arrear; overdue; as, back rent.
3. Moving or operating backward; as, back action.
{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.]
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.
2. The woof in woven fabrics.
3. (Brewing) Prepared wort added to ale to cleanse it.
{Back filling}. (Arch.) See under {Back}, a.