What does "frightful" mean?

Frightful: Full of that which causes fright; exciting alarm; impressing terror; shocking; as, a frightful chasm, or tempest; a frightful appearance. -- Frightful, Dreadful, Awful. These words all express fear. In frightful, it is a sudden emotion; in dreadful, it is deeper and more prolonged; in awful, the fear is mingled with the emotion of awe, which subdues us before the presence of some invisible power. An accident may be frightful; the approach of death is dreadful to most men; the convulsions of the earthquake are awful.