1660s, "frightening," from Latin terrificus "causing terror or fear, frightful," from terrere "fill with fear" (see terrible) + combining form of facere "to make" (from PIE root *dhe- "to set, put"). Weakened sensed of "very great, severe" (as in terrific headache) appeared 1809; inverted colloquial sense of "excellent" began 1888. Related: Terrifically.
