The Collaborative International Dictionary of English v.0.48:

Thwart \Thwart\, v. t. [imp. & p. p. Thwarted; p. pr. & vb. n.
   Thwarting.]
   1. To move across or counter to; to cross; as, an arrow
      thwarts the air. [Obs.]
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            Swift as a shooting star
            In autumn thwarts the night.          --Milton.
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   2. To cross, as a purpose; to oppose; to run counter to; to
      contravene; hence, to frustrate or defeat.
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            If crooked fortune had not thwarted me. --Shak.
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            The proposals of the one never thwarted the
            inclinations of the other.            --South.
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WordNet (r) 3.0 (2006):

thwarting
    adj 1: preventing realization or attainment of a desire [syn:
           frustrating, frustrative, thwarting]
    n 1: an act of hindering someone's plans or efforts [syn:
         frustration, thwarting, foiling]