Here's the first verse of the Pentangle version:-
There lived a lady by the North sea shore
(Lay the bent to the bonnie broom)
Two daughters were the babes she bore
(Fa la la la la la la la la la)
The word "bent" is probably the dialect word for hillside or grassy tract or possibly stiff grass, and "broom" is probably the (yellow) flowering plant. Not that it makes much sense anyway.
Anyone want the rest of the words?