The Collaborative International Dictionary of English v.0.48:

Guise \Guise\ (g[imac]z), n. [OE. guise, gise, way, manner, F.
   guise, fr. OHG. w[imac]sa, G. weise. See Wise, n.]
   1. Customary way of speaking or acting; custom; fashion;
      manner; behavior; mien; mode; practice; -- often used
      formerly in such phrases as: at his own guise; that is, in
      his own fashion, to suit himself. --Chaucer.
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            The swain replied, "It never was our guise
            To slight the poor, or aught humane despise."
                                                  --Pope.
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   2. External appearance in manner or dress; appropriate
      indication or expression; garb; shape.
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            As then the guise was for each gentle swain.
                                                  --Spenser.
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            A . . . specter, in a far more terrific guise than
            any which
            ever yet have overpowered the imagination. --Burke.
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   3. Cover; cloak; as, under the guise of patriotism.
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WordNet (r) 3.0 (2006):

guise
    n 1: an artful or simulated semblance; "under the guise of
         friendship he betrayed them" [syn: guise, pretense,
         pretence, pretext]