"Acaso": Perhap, Perhaps not

Question

When I look up the word "acaso" on the Spanishdict.com dictionary, the primary definition is "perhaps." Below is the example for this definition:

¿acaso no lo sabías? -> are you trying to tell me you didn't know?

The translation of the phrase does not contain the world "perhaps." Is it more a marker for presupposition in Spanish sentences? Can you clarify please?

Answer 1

....and remember "por si acaso" means "just in case."

Welcome to the forum.

Answer 2

According to Rae (see No 3) it can mean quizá or tal vez

acaso. (De caso).

1. m. Casualidad, suceso imprevisto.

2. adv. m. desus. Por casualidad, accidentalmente.

3. adv. duda Quizá, tal vez.

1. adv. neg. Ec. no (? indica la falta de lo significado por el verbo). Acaso he podido dormir.