9-11 vs terrorist act

9-11 and terrorist act both are nouns.

Word	Noun	Adjective	Verb	Adverb
9-11	Yes	No	No	No
terrorist act	Yes	No	No	No

9-11 (noun)	terrorist act (noun)
the day in 2001 when Arab suicide bombers hijacked United States airliners and used them as bombs	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