Source : Webster's Revised Unabridged Dictionary (1913)

Blab \Blab\, v. t. [imp. & p. p. {Blabbed} (?); p. pr. & vb. n.
   {Blabbing}.] [Cf. OE. blaberen, or Dan. blabbre, G. plappern,
   Gael. blabaran a stammerer; prob. of imitative origin. Cf.
   also {Blubber}, v.]
   To utter or tell unnecessarily, or in a thoughtless manner;
   to publish (secrets or trifles) without reserve or
   discretion. --Udall.

         And yonder a vile physician blabbing The case of his
         patient.                                 --Tennyson.

Source : WordNet®

blab
     v 1: divulge confidential information or secrets;  "Be
          careful--his secretary talks" [syn: {spill the beans}, {let
          the cat out of the bag}, {talk}, {tattle}, {peach}, {babble},
           {sing}, {babble out}, {blab out}] [ant: {keep quiet}]
     2: speak (about unimportant matters) rapidly and incessantly
        [syn: {chatter}, {piffle}, {palaver}, {prate}, {tittle-tattle},
         {twaddle}, {clack}, {maunder}, {prattle}, {gibber}, {tattle},
         {blabber}, {gabble}]
     [also: {blabbing}, {blabbed}]

blabbing
     See {blab}