The Collaborative International Dictionary of English v.0.48:

Roarer \Roar"er\, n.
   1. One who, or that which, roars. Specifically:
      (a) A riotous fellow; a roaring boy.
          [1913 Webster]

                A lady to turn roarer, and break glasses.
                                                  --Massinger.
          [1913 Webster]
      (b) (Far.) A horse subject to roaring. See Roaring, 2.
          [1913 Webster]

   2. (Zool.) The barn owl. [Prov. Eng.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

roarer
    n 1: someone who communicates vocally in a very loud voice [syn:
         roarer, bawler, bellower, screamer, screecher,
         shouter, yeller]