The Collaborative International Dictionary of English v.0.48:

Treble \Tre"ble\, v. t. [imp. & p. p. Trebled; p. pr. & vb. n.
   Trebling.]
   1. To make thrice as much; to make threefold. "Love trebled
      life." --Tennyson.
      [1913 Webster]

   2. To utter in a treble key; to whine. [Obs.]
      [1913 Webster]

            He outrageously
            (When I accused him) trebled his reply. --Chapman.
      [1913 Webster]