It is sort if like saying I think: I dare say your wrong. I dare say he doesn't know what he is doing. it also can be an exclaimation: I dare say! which sort of means : Really?!! It isn't used in America anymore, I dont know of it is in Britain.

To dare - atreverse de Por ejemplo: No me atrevo decirte que te amo - I don't dare to say you "I love you". No me atrevo ir al dentista. - I don't dare go to dentist. ¿Entiendes? Si tienes algúna duda más, no dude en preguntarme. ¡Que tengas un día genial!