terrorism

As nouns the difference between terrorism and megaterror

is that terrorism is the deliberate commission of an act of violence to create an emotional response through the suffering of the victims in the furtherance of a political or social agenda while megaterror is (informal) large-scale terrorism.

As nouns the difference between terrorism and counterterrorist

is that terrorism is the deliberate commission of an act of violence to create an emotional response through the suffering of the victims in the furtherance of a political or social agenda while counterterrorist is a person involved in counter-terrorism, who works against terrorists.

As an adjective counterterrorist is

intended to combat terrorism.