The Collaborative International Dictionary of English v.0.48:

Tax \Tax\ (t[a^]ks), v. t. [imp. & p. p. Taxed; p. pr. & vb.
   n. Taxing.] [Cf. F. taxer. See Tax, n.]
   1. To subject to the payment of a tax or taxes; to impose a
      tax upon; to lay a burden upon; especially, to exact money
      from for the support of government.
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            We are more heavily taxed by our idleness, pride,
            and folly than we are taxed by government.
                                                  --Franklin.
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   2. (Law) To assess, fix, or determine judicially, the amount
      of; as, to tax the cost of an action in court.
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   3. To charge; to accuse; also, to censure; -- often followed
      by with, rarely by of before an indirect object; as, to
      tax a man with pride.
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            I tax you, you elements, with unkindness. --Shak.
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            Men's virtues I have commended as freely as I have
            taxed their crimes.                   --Dryden.
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            Fear not now that men should tax thine honor. --M.
                                                  Arnold.
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WordNet (r) 3.0 (2006):

taxing
    adj 1: not easily borne; wearing; "the burdensome task of
           preparing the income tax return"; "my duties weren't
           onerous; I only had to greet the guests"; "a taxing
           schedule" [syn: burdensome, onerous, taxing]