The Collaborative International Dictionary of English v.0.48:

Orderly \Or"der*ly\, a.
   1. Conformed to order; in order; regular; as, an orderly
      course or plan. --Milton.
      [1913 Webster]

   2. Observant of order, authority, or rule; hence, obedient;
      quiet; peaceable; not unruly; as, orderly children; an
      orderly community.
      [1913 Webster]

   3. Performed in good or established order; well-regulated.
      "An orderly . . . march." --Clarendon.
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   4. Being on duty; keeping order; conveying orders.
      "Aids-de-camp and orderly men." --Sir W. Scott.
      [1913 Webster]

   Orderly book (Mil.), a book for every company, in which the
      general and regimental orders are recorded.

   Orderly officer, the officer of the day, or that officer of
      a corps or regiment whose turn it is to supervise for the
      day the arrangements for food, cleanliness, etc. --Farrow.

   Orderly room.
      (a) The court of the commanding officer, where charges
          against the men of the regiment are tried.
      (b) The office of the commanding officer, usually in the
          barracks, whence orders emanate. --Farrow.

   Orderly sergeant, the first sergeant of a company.
      [1913 Webster]

WordNet (r) 3.0 (2006):

orderly sergeant
    n 1: the first sergeant of a company; duties formerly included
         the conveyance of orders