The Collaborative International Dictionary of English v.0.48:

Vail \Vail\, n. [Aphetic form of avail, n.]
   [1913 Webster]
   1. Avails; profit; return; proceeds. [Obs.]
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            My house is as 'twere the cave where the young
            outlaw hoards the stolen vails of his occupation.
                                                  --Chapman.
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   2. An unexpected gain or acquisition; a casual advantage or
      benefit; a windfall. [Obs.]
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   3. Money given to servants by visitors; a gratuity; --
      usually in the plural. [Written also vale.] --Dryden.
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The Collaborative International Dictionary of English v.0.48:

Vail \Vail\, v. t. [Aphetic form of avale. See Avale, Vale.]
   [Written also vale, and veil.]
   1. To let fall; to allow or cause to sink. [Obs.]
      [1913 Webster]

            Vail your regard
            Upon a wronged, I would fain have said, a maid!
                                                  --Shak.
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   2. To lower, or take off, in token of inferiority, reverence,
      submission, or the like.
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            France must vail her lofty-plumed crest! --Shak.
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            Without vailing his bonnet or testifying any
            reverence for the alleged sanctity of the relic.
                                                  --Sir. W.
                                                  Scott.
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The Collaborative International Dictionary of English v.0.48:

Vail \Vail\ (v[=a]l), v. i.
   To yield or recede; to give place; to show respect by
   yielding, uncovering, or the like. [Written also vale, and
   veil.] [Obs.]
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         Thy convenience must vail to thy neighbor's necessity.
                                                  --South.
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The Collaborative International Dictionary of English v.0.48:

Vale \Vale\ (v[=a]l), n. [OE. val, F. val, L. vallis; perhaps
   akin to Gr. 'e`los low ground, marsh meadow. Cf. Avalanche,
   Vail to lower, Valley.]
   A tract of low ground, or of land between hills; a valley. "
   Make me a cottage in the vale." --Tennyson.
   [1913 Webster]

         Beyond this vale of tears there is a life above.
                                                  --Montgomery.
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         In those fair vales, by nature formed to please.
                                                  --Harte.
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   Note: Vale is more commonly used in poetry, and valley in
         prose and common discourse.
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   Syn: Valley; dingle; dell; dale.
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The Collaborative International Dictionary of English v.0.48:

Vale \Vale\, n.
   See 2d Vail, 3.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vale
    n 1: a long depression in the surface of the land that usually
         contains a river [syn: valley, vale]