Weren't they one-piece butts too ? Viking merry widows were .Merry widow does not have a splice or points of any kind.
Original (BBC) merry widows had a wrap.
Modern often have solid wood of different color(species) in the wrap area.
Tend to be a way to feature really nice natural wood pieces with minimal decoration other than sometimes ringwork.
Per the direct Q in your title, some seem to use the terms interchangeably.
However, to me, based on original in BBC catalogs, a Merry has distinctive sections of forearm, handle, buttsleeve, with a handle area that looks like a wrap, whether solid wood, or leather.
Then again i'm just an occasional amateur maker solely of FS sneakies.
Weren't they one-piece butts too ? Viking merry widows were .