The Collaborative International Dictionary of English v.0.48:

Balk \Balk\ (b[add]k), n. [AS. balca beam, ridge; akin to Icel.
   b[=a]lkr partition, bj[=a]lki beam, OS. balko, G. balken; cf.
   Gael. balc ridge of earth between two furrows. Cf. Balcony,
   Balk, v. t., 3d Bulk.]
   1. A ridge of land left unplowed between furrows, or at the
      end of a field; a piece missed by the plow slipping aside.
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            Bad plowmen made balks of such ground. --Fuller.
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   2. A great beam, rafter, or timber; esp., the tie-beam of a
      house. The loft above was called "the balks."
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            Tubs hanging in the balks.            --Chaucer.
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   3. (Mil.) One of the beams connecting the successive supports
      of a trestle bridge or bateau bridge.
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   4. A hindrance or disappointment; a check.
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            A balk to the confidence of the bold undertaker.
                                                  --South.
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   5. A sudden and obstinate stop; a failure.
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   6. (Baseball) A deceptive gesture of the pitcher, as if to
      deliver the ball. It is illegal and is penalized by
      allowing the runners on base to advance one base.
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   Balk line (Billiards), a line across a billiard table near
      one end, marking a limit within which the cue balls are
      placed in beginning a game; also, a line around the table,
      parallel to the sides, used in playing a particular game,
      called the balk line game.
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The Collaborative International Dictionary of English v.0.48:

Balk \Balk\, v. i.
   1. To engage in contradiction; to be in opposition. [Obs.]
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            In strifeful terms with him to balk.  --Spenser.
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   2. To stop abruptly and stand still obstinately; to jib; to
      stop short; to swerve; as, the horse balks.
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   Note: This has been regarded as an Americanism, but it occurs
         in Spenser's "Fa["e]rie Queene," Book IV., 10, xxv.
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               Ne ever ought but of their true loves talkt,
               Ne ever for rebuke or blame of any balkt.
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   3. (Baseball) to commit a balk[6]; -- of a pitcher.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Balk \Balk\, v. t. [imp. & p. p. Balked (b[add]kt); p. pr. &
   vb. n. Balking.] [From Balk a beam; orig. to put a balk
   or beam in one's way, in order to stop or hinder. Cf., for
   sense 2, AS. on balcan legan to lay in heaps.]
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   1. To leave or make balks in. [Obs.] --Gower.
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   2. To leave heaped up; to heap up in piles. [Obs.]
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            Ten thousand bold Scots, two and twenty knights,
            Balk'd in their own blood did Sir Walter see.
                                                  --Shak.
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   3. To omit, miss, or overlook by chance. [Obs.]
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   4. To miss intentionally; to avoid; to shun; to refuse; to
      let go by; to shirk. [Obs. or Obsolescent]
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            By reason of the contagion then in London, we balked
            the inns.                             --Evelyn.
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            Sick he is, and keeps his bed, and balks his meat.
                                                  --Bp. Hall.
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            Nor doth he any creature balk,
            But lays on all he meeteth.           --Drayton.
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   5. To disappoint; to frustrate; to foil; to baffle; to
      thwart; as, to balk expectation.
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            They shall not balk my entrance.      --Byron.
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The Collaborative International Dictionary of English v.0.48:

Balk \Balk\, v. i. [Prob. from D. balken to bray, bawl.]
   To indicate to fishermen, by shouts or signals from shore,
   the direction taken by the shoals of herring.
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WordNet (r) 3.0 (2006):

balk
    n 1: the area on a billiard table behind the balkline; "a player
         with ball in hand must play from the balk" [syn: balk,
         baulk]
    2: something immaterial that interferes with or delays action or
       progress [syn: hindrance, hinderance, deterrent,
       impediment, balk, baulk, check, handicap]
    3: one of several parallel sloping beams that support a roof
       [syn: rafter, balk, baulk]
    4: an illegal pitching motion while runners are on base
    v 1: refuse to comply [syn: resist, balk, baulk, jib]

Moby Thesaurus II by Grady Ward, 1.0:

137 Moby Thesaurus words for "balk":
   baffle, bafflement, balk at, balking, be unwilling, beam, beat,
   begrudge, betrayed hope, bevue, bilk, blast, blasted expectation,
   blighted hope, blow, boggle, brave, buffet, cast down, challenge,
   check, checkmate, circumvent, comedown, confound, confounding,
   confront, confusion, contravene, counter, counteract, countermand,
   counterwork, cross, cruel disappointment, dash, dashed hope,
   decline, defeat, defeat expectation, defy, destroy, die hard,
   disappoint, disappointment, discomfit, discomfiture, disconcert,
   disconcertion, discountenance, dish, disillusion, disillusionment,
   disrupt, dissatisfaction, dissatisfy, elude, failure,
   fallen countenance, false move, false step, fiasco, fizzle, flinch,
   flummox, foil, foiling, forlorn hope, frustrate, frustration, gag,
   grudge, hang back, hold out, hope deferred, inadvertence,
   inadvertency, jib, knock the chocks, lapse, lapsus calami,
   lapsus linguae, let down, letdown, loose thread, mind, mirage,
   miscue, misstep, nonplus, not budge, not care to, not feel like,
   object to, omission, oversight, perplex, persevere, quail, rebuff,
   recoil, refuse, repulse, reversal, reverse, rout, ruin, sabotage,
   scotch, scruple, setback, shrink, shy, slip, slipup,
   sore disappointment, spike, spoil, stand out, stand pat, stick,
   stickle, stonewall, strain, stumble, stump, take no denial,
   tantalization, tantalize, tease, thwart, thwarting, trip,
   turn down, upset, would rather not, wrong step