The Collaborative International Dictionary of English v.0.48:

Vexillum \Vex*il"lum\, n.; pl. Vexilla. [L., a standard, a
   flag.]
   1. (Rom. Antiq.)
      (a) A flag or standard.
      (b) A company of troops serving under one standard.
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   2. (Eccl.)
      (a) A banner.
      (b) The sign of the cross.
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   3. (Bot.) The upper petal of a papilionaceous flower; the
      standard.
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   4. (Zool.) The rhachis and web of a feather taken together;
      the vane.
      [1913 Webster]