古罗马历中自三、五、七、十各月的十五日起算的前第九日即三、五、七、十各月的第七日；其它各月的第五日 The ninth day before the ides of a month; in the ancient Roman calendar, the seventh day of March, May, July, or October and the fifth day of the other months.
九和弦由第三、第七和第九三个基础音组成的和弦 A chord consisting of a root with its third, seventh, and ninth.
他在40个人的班级里排在第九名。 He took the ninth position in his class of forty.
