if something is reasonable, there are good reasons for thinking that it is true or correcta reasonable explanation/excuse: I’m sure there’s a perfectly reasonable explanation for his absence.
It’s reasonable to assume that these measures will prove successful.
They had reasonable grounds for taking action.
beyond (a) reasonable doubt (=so that there is little possibility of something not being true): The prosecution must prove their case beyond reasonable doubt.
a reasonable chance/prospect: We still had a reasonable prospect of finding a job locally.