The Collaborative International Dictionary of English v.0.48:

Ho \Ho\, Hoa \Hoa\ (h[=o]), interj. [Cf. F. & G. ho.]
   1. Halloo! attend! -- a call to excite attention, or to give
      notice of approach. "What noise there, ho?" --Shak. "Ho!
      who's within?" --Shak.
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   2. [Perhaps corrupted fr. hold; but cf. F. hau stop! and E.
      whoa.] Stop! stand still! hold! -- a word now used by
      teamsters, but formerly to order the cessation of
      anything. [Written also whoa, and, formerly, hoo.]
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            The duke . . . pulled out his sword and cried "Hoo!"
                                                  --Chaucer.
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            An herald on a scaffold made an hoo.  --Chaucer.
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The Collaborative International Dictionary of English v.0.48:

Hoo \Hoo\, interj.
   1. See Ho. [Obs.] --Chaucer.
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   2. Hurrah! -- an exclamation of triumphant joy. --Shak.
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