Reginzo

The first element is equal to Old Dutch *regin (“advice”). The second element, -zo, seems out of place in Old Dutch, which might point at a borrowing from Old High German Reginzo. This idea can be supported by the fact that names ending in -zo/-za are almost never found before the 10th century and only rarely in Holland (but very commonly in the south and east of the Old Dutch language area). Its origin, however, is unclear, and both Old Dutch and Old Saxon are lacking in obvious proofs of a cognate along the lines of -to/-ta. The suffix originating from Old Dutch seems less likely, because of the form's relatively late appearence and very ununiform distribution.