9-11 vs Sept. 11

9-11 and Sept. 11 both are nouns.

Word	Noun	Adjective	Verb	Adverb
9-11	Yes	No	No	No
Sept. 11	Yes	No	No	No

As nouns, 9-11 and Sept. 11 are synonyms defined as:

9-11 and Sept. 11: the day in 2001 when Arab suicide bombers hijacked United States airliners and used them as bombs

Other synonyms of 9-11 include 9/11, Sep 11, September 11, September 11 attacks.

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