The Collaborative International Dictionary of English v.0.48:

Spoonful \Spoon"ful\ (-f[.u]l), n.; pl. Spoonfuls (-f[.u]lz).
   1. The quantity which a spoon contains, or is able to
      contain; as, a teaspoonful; a tablespoonful.
      [1913 Webster]

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