1The native Japanese way of counting "six" items, one of the traditional 一つ・二つ… counting words.
かごの中にみかんが六つ入っている。
There are six mandarin oranges in the basket.
テーブルに椅子を六つ用意した。
I prepared six chairs at the table.
六つのグループに分かれて作業を進めた。
We split into six groups and got to work.
2A colloquial way of saying someone is six years old, often used when talking about a young child's age.
うちの子は今年で六つになる。
My child will turn six this year.
六つの子にしてはしっかりしている。
She's quite mature for a six-year-old.
3An old way of naming the time under the Edo-period unequal-hour system, roughly corresponding to six o'clock. Essentially unused in modern speech; it survives only in historical fiction and period contexts.