NOUN (3)

1. a negotiator who hopes to gain concessions by refusing to come to terms;
- Example: "their star pitcher was a holdout for six weeks"

2. a refusal by a negotiator to come to terms in the hope of obtaining a better deal;

3. the act of hiding playing cards in a gambling game so they are available for personal use later;

The Collaborative International Dictionary of English v.0.48:

holdout \holdout\ n.
   1. a negotiator who hopes to gain concessions by refusing to
      come to terms after most other participants have signed an
      agreement; as, their star pitcher was a holdout for six
      weeks.
      [WordNet 1.5]

   2. a refusal by a negotiator to come to terms in the hope of
      obtaining a better deal.
      [WordNet 1.5]

   3. the act of hiding playing cards in a gambling game so they
      are available for personal use later.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

holdout
    n 1: a negotiator who hopes to gain concessions by refusing to
         come to terms; "their star pitcher was a holdout for six
         weeks"
    2: a refusal by a negotiator to come to terms in the hope of
       obtaining a better deal
    3: the act of hiding playing cards in a gambling game so they
       are available for personal use later