Sep 11 vs September 11 attacks

Sep 11 and September 11 attacks both are nouns.

Word	Noun	Adjective	Verb	Adverb
Sep 11	Yes	No	No	No
September 11 attacks	Yes	No	No	No

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

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

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

Sep 11 (noun)	September 11 attacks (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