(ひと)

ひとつ
noun
one (thing)
1. one (thing)
The number one when counting things using native Japanese numbers.
りんご(ひと)ください
One apple, please.
Only one is left.
I have one question.
Not even one is left.
I'll check them one by one.
They're one grade above.
I have one favor to ask.
2. one year old
Age of one year (informal counting).
The child is one year old.
My daughter turned one.
They can talk even though they're only one.
The baby turned one, so we had a celebration.
Our child took their first steps at age one.

(ひと)つ is the native Japanese number 'one,' used for counting general items and as part of many set expressions.

NATIVE COUNTING (1-10):

COMMON PATTERNS:

AGE:
Used informally for age one: 子供(こども)(ひと)なった (the child turned one). This native system (ひとつ, ふたつ...) is used for young children's ages up to about nine.

USAGE:
This native counting system is used for general items when no specific counter applies, or when the counter is unknown.