The Collaborative International Dictionary of English v.0.48:

Back \Back\ (b[a^]k), v. t. [imp. & p. p. Backed (b[a^]kt); p.
   pr. & vb. n. Backing.]
   [1913 Webster]
   1. To get upon the back of; to mount.
      [1913 Webster]

            I will back him [a horse] straight.   --Shak.
      [1913 Webster]

   2. To place or seat upon the back. [R.]
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            Great Jupiter, upon his eagle backed,
            Appeared to me.                       --Shak.
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   3. To drive or force backward; to cause to retreat or recede;
      as, to back oxen.
      [1913 Webster]

   4. To make a back for; to furnish with a back; as, to back
      books.
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   5. To adjoin behind; to be at the back of.
      [1913 Webster]

            A garden . . . with a vineyard backed. --Shak.
      [1913 Webster]

            The chalk cliffs which back the beach. --Huxley.
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   6. To write upon the back of; as, to back a letter; to
      indorse; as, to back a note or legal document.
      [1913 Webster]

   7. To support; to maintain; to second or strengthen by aid or
      influence; as, to back a friend. "The Parliament would be
      backed by the people." --Macaulay.
      [1913 Webster]

            Have still found it necessary to back and fortify
            their laws with rewards and punishments. --South.
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            The mate backed the captain manfully. --Blackw. Mag.
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   8. To bet on the success of; -- as, to back a race horse.
      [1913 Webster]

   To back an anchor (Naut.), to lay down a small anchor ahead
      of a large one, the cable of the small one being fastened
      to the crown of the large one.

   To back the field, in horse racing, to bet against a
      particular horse or horses, that some one of all the other
      horses, collectively designated "the field", will win.

   To back the oars, to row backward with the oars.

   To back a rope, to put on a preventer.

   To back the sails, to arrange them so as to cause the ship
      to move astern.

   To back up, to support; to sustain; as, to back up one's
      friends.

   To back a warrant (Law), is for a justice of the peace, in
      the county where the warrant is to be executed, to sign or
      indorse a warrant, issued in another county, to apprehend
      an offender.

   To back water (Naut.), to reverse the action of the oars,
      paddles, or propeller, so as to force the boat or ship
      backward.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Backing \Back"ing\, n.
   1. The act of moving backward, or of putting or moving
      anything backward.
      [1913 Webster]

   2. That which is behind, and forms the back of, anything,
      usually giving strength or stability.
      [1913 Webster]

   3. Support or aid given to a person or cause.
      [1913 Webster]

   4. (Bookbinding) The preparation of the back of a book with
      glue, etc., before putting on the cover.
      [1913 Webster]

WordNet (r) 3.0 (2006):

backing
    n 1: the act of providing approval and support; "his vigorous
         backing of the conservatives got him in trouble with
         progressives" [syn: backing, backup, championship,
         patronage]
    2: something forming a back that is added for strengthening
       [syn: backing, mount]
    3: financial resources provided to make some project possible;
       "the foundation provided support for the experiment" [syn:
       support, financial support, funding, backing,
       financial backing]

Moby Thesaurus II by Grady Ward, 1.0:

317 Moby Thesaurus words for "backing":
   Brownian movement, Smyth sewing, abetment, about-face, about-turn,
   advance, advocacy, advocate, advocating, aegis, affirmation, aid,
   alpenstock, angular motion, approval, approving, arm, ascending,
   ascent, assistance, athletic supporter, attestation, auspices,
   authentication, axial motion, back, back track, back trail,
   backbone, backflowing, backing off, backing out, backing up,
   backsliding, backup, backward motion, bandeau, bearer, bearing,
   bearing out, bibliofilm, bibliopegy, binder board, binding, bipack,
   black-and-white film, bolstering, book cloth, book cover,
   book jacket, bookbinding, bookcase, bra, brace, bracer, bracket,
   brassiere, bushing, buttress, buttressing, cane, capitalization,
   care, career, carriage, carrier, carrying, cartridge, case,
   casemaking, casing-in, certification, cervix, championship,
   charity, chassis, circumstantiation, climbing, collating,
   collating mark, color film, color negative film, confirmation,
   cooperation, corroboration, corroboratory evidence, corset,
   countenance, course, cover, crook, crutch, current,
   deficit financing, descending, descent, disenchantment,
   documentation, dope, downward motion, drift, driftage, dry plate,
   dust cover, dust jacket, ebbing, emulsion, encouragement,
   endorsement, favor, favorable, favoring, film, financial backing,
   financial support, financing, flight, flip-flop, flow, flux,
   folding, footband, fortification, forward motion, fosterage,
   foundation garment, frame, fulcrum, funding, funds, gathering,
   girdle, gluing-off, goodwill, grant, grubstake, guidance, guy,
   guywire, hard binding, headband, help, infrastructure, interest,
   investment, jacket, jock, jockstrap, lapse, library binding,
   lining, lining-up, mainstay, maintainer, maintenance, mast,
   mechanical binding, microfilm, money, monochromatic film,
   moral support, motion-picture film, mount, mounting, neck,
   negative, niggerhead, oblique motion, ongoing, onrush,
   orthochromatic film, pack, panchromatic film, passage, patronage,
   patronization, perfect binding, photographic paper,
   plastic binding, plate, plunging, printing paper, pro, progress,
   proof, prop, proving, proving out, provision of capital,
   psychological support, radial motion, random motion, ratification,
   recidivation, recidivism, reclamation, reconversion, reflowing,
   refluence, reflux, regress, regression, rehabilitation, reinforce,
   reinforcement, reinforcer, reinstatement, relapse, reliance, rest,
   resting place, restitution, restoration, retrocession,
   retrogradation, retrogression, retroversion, return, returning,
   reversal, reverse, reversing, reversion, reverting, revulsion,
   rigging, right-about, right-about-face, rising, roll, rounding,
   run, rush, saddle stitching, seconding, security blanket, set,
   setting, sewing, shoulder, shroud, side sewing, sideward motion,
   signature, sinking, skeleton, slipcase, slipcover, slipping back,
   smashing, soaring, soft binding, sound film, sound track,
   sound-on-film, soundstripe, spine, spiral binding, sponsorship,
   sprit, staff, stake, stamping, standing rigging, stapling, stave,
   stay, sternway, stick, stiffener, stream, strengthener,
   strengthening, subsiding, subsidy, substantiation, subvention,
   succor, support, supporter, supporting, supporting evidence,
   supportive relationship, supportive therapy, sustainer, sustaining,
   sustainment, sustenance, sustentation, swingaround, sympathy,
   tailband, tipping, traject, trajet, trend, trimming, tripack, turn,
   turnabout, turnaround, tutelage, underframe, undergirding,
   upholder, upholding, upkeep, upward motion, validation, vehicle,
   verification, volte-face, walking stick, well-disposed,
   well-inclined, wire stitching, wrapper



Bouvier's Law Dictionary, Revised 6th Ed (1856):

BACKING, crim. law practice. Backing a warrant occurs whenever it becomes
necessary to execute it out of the jurisdiction of the magistrate who
granted it; as when an offender escapes out of the county in which he
committed the offence with which he is charged, into another county. In such
a case, a magistrate of the county in which the offender may, be found,
endorses, or writes his name on the back of the warrant, and thereby gives
authority to execute it within his jurisdiction. This is called backing the
warrant. This may be from county to county, if necessary.