The Collaborative International Dictionary of English v.0.48:

Drivel \Driv"el\, v. i. [imp. & p. p. Driveledor Drivelled;
   p. pr. & vb. n. Driveling or Drivelling.] [Cf. OE.
   dravelen, drabelen, drevelen, drivelen, to slaver, and E.
   drabble. Cf. Drool.]
   1. To slaver; to let spittle drop or flow from the mouth,
      like a child, idiot, or dotard.
      [1913 Webster]

   2. [Perh. a different word: cf. Icel. drafa to talk thick.]
      To be weak or foolish; to dote; as, a driveling hero;
      driveling love. --Shak. Dryden.
      [1913 Webster]