The Collaborative International Dictionary of English v.0.48:

Rogation \Ro*ga"tion\, n. [L. rogatio, fr. rogare, rogatum, to
   ask, beg, supplicate: cf. F. rogation. Cf. Abrogate,
   Arrogant, Probogue.]
   1. (Rom. Antiq.) The demand, by the consuls or tribunes, of a
      law to be passed by the people; a proposed law or decree.
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   2. (Eccl.) Litany; supplication.
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            He perfecteth the rogations or litanies before in
            use.                                  --Hooker.
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   Rogation days (Eccl.), the three days which immediately
      precede Ascension Day; -- so called as being days on
      which the people, walking in procession, sang litanies of
      special supplication.

   Rogation flower (Bot.), a European species of milkwort
      (Polygala vulgaris); -- so called from its former use
      for garlands in Rogation week. --Dr. Prior.

   Rogation week, the second week before Whitsunday, in which
      the Rogation days occur.
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WordNet (r) 3.0 (2006):

rogation
    n 1: a solemn supplication ceremony prescribed by the church