"Rebecca = knotted chord"? That's the nice version!
It's more usually said to mean noose 
although I have seen it glossed over as "captivator" (gotta give them marks for trying there!)
I've also read somewhere that it means "heifer"! Also not so great.
Although a book I read said that it's unlikely that that any of these were actually it's orginal meaning - it's such an old name the meaning may well have got lost over time.
It can also allude to the Rebecca Riots (which happenned in Wales in the first half of the 19th century) and were about the people standing up to the (generally English) landowners, and which is a great association I think 
"Rebecca" in the riots, was a part played by a man. "Rebecca" would be dressed as an old woman, and would ride up to a toll gate on a horse. "She" would get off the horse, and would then act out a little play - with the other rioters. She would say that she was old and couldn't get through the gate. The rioters would help her pass by destroying it.
So, you could also say Rebecca is a Welsh transvestite, I think that's a great assocation too