-Nine is the highest single-digit number in the decimal system.
-Nine is the number of musicians in a nonet.
-Nine judges sit on the United States Supreme Court.
-The New Testament is divided into nine subsections.
-In music theory a Ninth is the ninth Note of a musical scale.
-Someone dressed "to the nines" is dressed up as much as they can be.
-Nine months is the average number of months per school year that most primary and secondary students are required to attend.
-In Greek mythology, nine goddesses called the Muses were responsible for inspiring the art of musicians, artists, and writers.
-Nine (九 Pinyin jiu) is considered a good number in Chinese culture because it sounds the same as the word "longlasting" (久 Pinyin jiu).
Number nine will put you on the spot.
Number nine will tie you up, oh, in a knot.
When you're tryin',
Multiplyin' by nine,
You might give it everything you've got
And still be stopped.
If you don't know some secret way you can check on,
You'll break your neck on
Naughty number nine
(excerpt from Naughty Number Nine – Schoolhouse Rock)