absurd, far-fetched, crazy
No, quince por cada diez empezaba a sonar completamente descabellado.
No, fifteen for every ten was starting to sound completely ridiculous.
Sonaba demasiado descabellado.
It sounded too far-fetched.
De entre todos nosotros, Tom tenía el humor más descabellado.
Of all of us, Tom had the most outlandish sense of humor.