The native Japanese numeral for nine, used for counting general items with the つ counter.
Please give me nine apples.
nine years old
Used to state a child's age, especially in traditional or formal contexts. In modern casual speech, 九歳 (きゅうさい) is also common.
My daughter will be nine years old this year.
twelve o'clock (old time system)
In the old Japanese temporal hour system, 九つ corresponded to the modern twelve o'clock (noon or midnight). This usage is now historical and rarely encountered outside explanations of the old system.
In the Edo period, noon was called 'kokonotsu'.
I bought nine apples.
My daughter will turn nine next month.