This is the 103rd most frequent Persian word.
تنها
Alone; only.
Here, "تنها" conveys the meaning of "only," specifying a limited amount of time.
او تنها دو ساعت برای این کار وقت دارد.
He has only two hours for this task.
In this context, "تنها" functions similarly to "only" or "just," emphasizing that it is nothing more than a story.
این تنها یک داستان است.
This is only a story.
In this sentence, "تنها" means "alone," describing the subject's action performed without company.