In honor of September, a yojijukugo with some nines in it!
Literally: nine – part – nine – smaller part [1/10 of a bu]
Alternately: 99%. Ninety-nine times out of a hundred. Almost certainly.
Notes: There is some danger here due to 分 also meaning 1%, so that the phrase can be misread as “a 9.9% chance.” However, in this case 分 means “one part (in ten),” and from this the meaning of something almost guaranteed to happen is born.