9-11 vs terrorist attack

9-11 and terrorist attack both are nouns.

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

9-11 (noun)	terrorist attack (noun)
the day in 2001 when Arab suicide bombers hijacked United States airliners and used them as bombs	a surprise attack involving the deliberate use of violence against civilians in the hope of attaining political or religious aims