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