September 11 attacks vs Sept. 11

September 11 attacks and Sept. 11 both are nouns.

Word	Noun	Adjective	Verb	Adverb
September 11 attacks	Yes	No	No	No
Sept. 11	Yes	No	No	No

As nouns, September 11 attacks and Sept. 11 are synonyms defined as:

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

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

September 11 attacks (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