you are right, it means 2 weeks,apparently it goes back to the 12 century meaning 14 nights in olde English. i never thought of it before. It is strange as you have now started me on a path to look at some of our sayings and try to find the origins of them.
This could be a good laugh for the forum to get the guys and Gals to come forward with unusual words and their origins.
The 2 best sayings over here in Ireland are:
see if you can figure out what these mean