This is the 4413th most frequent Japanese word.
四つ
"Four" or "four things."
Represents an age, specifically four years old.
その子は四つになるまでに歩けるようになりました。
That child learned to walk by the age of four.
Used as a counter for objects, indicating the number four.
私は四つのみかんを買いました。
I bought four oranges.
Used as a counter to specify the quantity of possible responses.