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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WordNet (r) 3.0 (2006):

balking
    adj 1: stopping short and refusing to go on; "a balking"; "a
           balky mule"; "a balky customer" [syn: balking, balky]