Source : Webster's Revised Unabridged Dictionary (1913)

Thwart \Thwart\, v. i.
   1. To move or go in an oblique or crosswise manner. [R.]

   2. Hence, to be in opposition; to clash. [R.]

            Any proposition . . . that shall at all thwart with
            internal oracles.                     --Locke.

Thwart \Thwart\, a. [OE. [thorn]wart, [thorn]wert, a. and adv.,
   Icel. [thorn]vert, neut. of [thorn]verr athwart, transverse,
   across; akin to AS. [thorn]weorh perverse, transverse, cross,
   D. dwars, OHG. dwerah, twerh, G. zwerch, quer, Dan. & Sw.
   tver athwart, transverse, Sw. tv["a]r cross, unfriendly,
   Goth. [thorn]wa['i]rhs angry. Cf. {Queer}.]
   1. Situated or placed across something else; transverse;
      oblique.

            Moved contrary with thwart obliquities. --Milton.

   2. Fig.: Perverse; crossgrained. [Obs.] --Shak.

Thwart \Thwart\, adv. [See {Thwart}, a.]
   Thwartly; obliquely; transversely; athwart. [Obs.] --Milton.

Thwart \Thwart\, prep.
   Across; athwart. --Spenser.

   {Thwart ships}. See {Athwart ships}, under {Athwart}.

Thwart \Thwart\, n. (Naut.)
   A seat in an open boat reaching from one side to the other,
   or athwart the boat.

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.]

            Swift as a shooting star In autumn thwarts the
            night.                                --Milton.

   2. To cross, as a purpose; to oppose; to run counter to; to
      contravene; hence, to frustrate or defeat.

            If crooked fortune had not thwarted me. --Shak.

            The proposals of the one never thwarted the
            inclinations of the other.            --South.

Source : WordNet®

thwart
     n : a crosspiece spreading the gunnels of a boat; used as a seat
         in a rowboat [syn: {cross thwart}]
     v : hinder or prevent (the efforts, plans, or desires) of; "What
         ultimately frustrated every challenger was Ruth's amazing
         September surge"; "foil your opponent" [syn: {queer}, {spoil},
          {scotch}, {foil}, {cross}, {frustrate}, {baffle}, {bilk}]