>Where as a week starts with Sunday. So sennight is seven days–but a week is from Sunday to Sunday?

Helen,

I agree in general with xara's response to your post, except for the bit about "next week" meaning Sunday to Saturday, similar to your definition above.

I am surprised that anyone still thinks about Sunday as being the start of the week - I thought it was an antiquated thing, presumably springing from the Christian religion and the importance of going to church on that day. For me, Monday is clearly the start of a new week. Sunday can't possibly be, as it is part of the "weekend".