The Collaborative International Dictionary of English v.0.48:

Blatter \Blat"ter\, v. i. [imp. & p. p. Blattered.] [L.
   blaterare to babble: cf. F. blat['e]rer to bleat.]
   To prate; to babble; to rail; to make a senseless noise; to
   patter. [Archaic] "The rain blattered." --Jeffrey.
   [1913 Webster]

         They procured . . . preachers to blatter against me, .
         . . so that they had place and time to belie me
         shamefully.                              --Latimer.
   [1913 Webster]