mouth·ful / ˈmou[unvoicedth]ˌfoŏl/ • n. (pl. -fuls) 1. a quantity of food or drink that fills or can be put into the mouth: he took a mouthful of beer savor the flavor of each mouthful.2. a long or complicated word or phrase that is difficult to say: “Galinsoga” was too much of a mouthful for most nonbotanists.PHRASES: give someone a mouthful inf. talk to or shout at someone in an angry, abusive, or severely critical way.say a mouthful inf. say something noteworthy.