only once
Te lo preguntaré una sola vez.
I'll ask you just once.
Tom no ha visto ni una sola vez a Mary.
Tom hasn't seen Mary even once.
Not once in a thousand years.
You think it's just a one-time thing.
Una sola vez no basta para poder juzgar.
Once is not enough to be able to judge.
— La vida de Adèle (2013)
Bastaba con decirte una sola vez las cosas.
It was enough to tell you things just once.
— Comer, beber, amar (1994)