reign of terror vs terrorist act

reign of terror and terrorist act both are nouns.

Word	Noun	Adjective	Verb	Adverb
reign of terror	Yes	No	No	No
terrorist act	Yes	No	No	No

reign of terror (noun)	terrorist act (noun)
any period of brutal suppression thought to resemble the Reign of Terror in France	the calculated use of violence (or the threat of violence) against civilians in order to attain goals that are political or religious or ideological in nature; this is done through intimidation or coercion or instilling fear