Well, there really should be no problem in believing that the "S" sound could change to a "Z" or vice versa over time. These are very similar sounds phonetically; the English "z" is simply the "voiced" form of "s", I believe. There are plenty of examples of these two sounds being substituted for one another. In Latin American Spanish, the "z" sound has been replaced by "s", so Hispanic parents in the USA feel free to do respellings such as Jezzica for Jessica
. In Reaney & Wilson
's A Dictionary of English Surnames, all six of the native English surnames that start with "Z" are explained as variations of more common surnames that start with "S".
As for the "o" -- I don't know how that particular letter would have come to be there, but the fact that there is a middle syllable may simply show that the name came into French from ancient Germanic instead of from modern German
. Both Hanks & Hodges' A Dictionary of Surnames
and my Dutch given name dictionary (by van der Schaar) give the most ancient Germanic form of Sieg- as "Sigi
-". German Names
(a surname dictionary) by Hans
Bahlow also gives several ancient forms of Sieg- names with middle syllables, such as Segimundus for Sigmund
, Sigeman for Siegmann, and Segewin and Sigewin for Siegwein. So it seems likely to me that both the modern German Sieglinde
and the modern French Segolene are derived from a very ancient Germanic form which was something like "Sigilindi".