Source : Webster's Revised Unabridged Dictionary (1913)

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

   2. Hence, a small quantity.

Source : WordNet®

mouthful
     n 1: the quantity that can be held in the mouth
     2: a small amount eaten or drunk; "take a taste--you'll like
        it" [syn: {taste}]