Pronunciation: (fēr'ful),[key] —adj. 1. causing or apt to cause fear; frightening: a fearful apparition. 2. feeling fear, dread, apprehension, or solicitude: fearful for his life; fearful lest he commit suicide. 3. full of awe or reverence: fearful of the Lord. 4. showing or caused by fear: fearful behavior. 5. extreme in size, intensity, or badness: a fearful head cold; fearful poverty.