Thanks, both Fred and Reinhard.

I'm happy to accept the correction that both bereave & Reiver originate from a common root rather than that the former "comes from" the latter. I'm not pedant enough to call Maddy Prior wrong on that ground.

But I'm still puzzled as to why both Maddy Prior and The Reiver Trail relate blackmail and Reiver etymologically. Presumably from a common source (bit like the surmised Q document of Jesus' sayings that both Matthew & Luke are supposed to have had access to). Interesting.

As to the identity of the two visitors in the song -- Reivers or not, I couldn't really care less.