(informal) next to nothing (very little)

(informal) if, in case

doubly, so as to make sure, so that there be absolutely no doubt / absolutely! with pleasure! yes please!

there was once…; once upon a time, there was… (traditional beginning of children’s stories, especially fairy tales)

(idiomatic) once and for all (finally, permanently, conclusively)

you only go around once, you only live once, YOLO

doing it once is all right, but let it not turn into a habit; it's ok this time, but let's not make a habit of it

Alternative form of une fois pour toutes

(figuratively) to think twice

once in a blue moon (very rarely or never)