The Collaborative International Dictionary of English v.0.48:

Mouthful \Mouth"ful\, n.; pl. Mouthfuls.
   1. As much as is usually put into the mouth at one time.
      [1913 Webster]

   2. Hence, a small quantity.
      [1913 Webster]

   3. A statement that has a profound truth in it; as, you said
      a mouthful! [informal]
      [PJC]