The Collaborative International Dictionary of English v.0.48:

Imposition \Im`po*si"tion\, n. [F., fr. L. impositio the
   application of a name to a thing. See Impone.]
   1. The act of imposing, laying on, affixing, enjoining,
      inflicting, obtruding, and the like. "From imposition of
      strict laws." --Milton.
      [1913 Webster]

            Made more solemn by the imposition of hands.
                                                  --Hammond.
      [1913 Webster]

   2. That which is imposed, levied, or enjoined; charge;
      burden; injunction; tax.
      [1913 Webster]

   3. (Eng. Univ.) An extra exercise enjoined on students as a
      punishment. --T. Warton.
      [1913 Webster]

   4. An excessive, arbitrary, or unlawful exaction; hence, a
      trick or deception put on laid on others; cheating; fraud;
      delusion; imposture.
      [1913 Webster]

            Reputation is an idle and most false imposition.
                                                  --Shak.
      [1913 Webster]

   5. (Eccl.) The act of laying on the hands as a religious
      ceremoy, in ordination, confirmation, etc.
      [1913 Webster]

   6. (Print.) The act or process of imosing pages or columns of
      type. See Impose, v. t., 4.

   Syn: Deceit; fraud; imposture. See Deception.
        [1913 Webster]

WordNet (r) 3.0 (2006):

imposition
    n 1: the act of imposing something (as a tax or an embargo)
         [syn: imposition, infliction]
    2: an uncalled-for burden; "he listened but resented the
       imposition"

Moby Thesaurus II by Grady Ward, 1.0:

189 Moby Thesaurus words for "imposition":
   Intertype, Linotype, Monotype, application, applying, assessment,
   assumption, atrocity, ballot-box stuffing, blackmail, bunco,
   burden, burthen, call, call for, cardsharping, cargo, cess, charge,
   cheat, cheating, claim, cold-type typesetting, composing,
   composing stick, composition, computerized typesetting,
   conscience money, contribution, cozenage, cross, cumbrance,
   deadweight, demand, demand for, diddle, diddling, difficulty,
   direct tax, disadvantage, dishonesty, disservice, dodge, draft,
   drain, dummy, duty, embarrassment, encroachment, encumbrance,
   enforcement, enforcing, entrance, entrenchment, exaction,
   extortion, extortionate demand, familiarity, fishy transaction,
   flam, flimflam, fraud, fraudulence, fraudulency, freight,
   furniture, galley chase, gerrymandering, graduated taxation, graft,
   great wrong, grievance, grift, gross injustice, gyp, gyp joint,
   hamper, handicap, heavy demand, hot-metal typesetting, hubris,
   illicit business, impediment, impedimenta, impingement, impost,
   imposture, inconvenience, incursion, indent, indirect tax,
   infiltration, inflicting, infliction, influx, infringement,
   injection, injury, injustice, inroad, insinuation,
   insistent demand, interference, interjection, interloping,
   interposition, interposure, interruption, intervention,
   introduction, intrusion, invasion, irruption, joint return,
   justification, lawlessness, laying on, layout, levy, liberties,
   liberty abused, license, licentiousness, line of type, load,
   lumber, miscarriage of justice, misuse, nonnegotiable demand,
   notice, obtrusion, onus, order, outrage, pack, penalty,
   photocomposition, photosetting, phototypesetter,
   phototypesetting machine, placement, placing, presumption,
   presumptuousness, progressive tax, promulgation, quoin, racket,
   raw deal, requirement, requisition, rush, rush order, scam,
   separate returns, setting, single tax, slug, supertax, surtax,
   swindle, tax, tax base, tax dodging, tax evasion, tax exemption,
   tax return, tax structure, tax withholding, tax-exempt status,
   taxable income, taxation, taxing, tithe, toll, trespass,
   trespassing, tribute, trouble, typesetting, typesetting machine,
   ultimatum, undue liberty, unlawful entry, warning, weight,
   white elephant, withholding tax, wrong



The Devil's Dictionary (1881-1906):

IMPOSITION, n.  The act of blessing or consecrating by the laying on
of hands -- a ceremony common to many ecclesiastical systems, but
performed with the frankest sincerity by the sect known as Thieves.

    "Lo! by the laying on of hands,"
        Say parson, priest and dervise,
    "We consecrate your cash and lands
        To ecclesiastical service.
    No doubt you'll swear till all is blue
    At such an imposition.  Do."
                                                          Pollo Doncas