Every Monday we will post an entry that hasn’t yet been published with a view towards harnessing the collective onomastic power of the internet. If you have any thoughts about the name’s origin, other variants it might be related to, other examples of its use, etc., please share them in the comments! If you wish to browse other Mystery Monday names, there is an index.
Today’s name is an early Germanic name found in Hamburg which is unusual in that we have a number of different examples of it in the same source, including one variant (Liebizo) which we aren’t entirely sure is the same name.
In fact, we aren’t sure anything about this name — is it dithematic? Is it a nickname? Have we guessed a good normalised form? — except that it is Germanic, and masculine.
If you’ve got any thoughts about the origin of this name, please share in the comments! We’d love to know.
Dictionary of Medieval Names from European Sources 
The person in question is Libentius I, archbishop of Hamburg 988-1013; see especially the footnote at the Liauizoni citation. The German Wikipedia article to which I linked notes that his name also appears as Libizo and Liawizo. Here he appears as Liebizo
He came from Raetia Curiensis or Upper Burgundy — loosely, Switzerland — so I expect that his name really was Germanic, and that we can probably ignore Libentius. The name is pretty clearly a diminutive in the common diminutive suffix -izo, and the base appears to be from PGmc. *leubaz ‘dear, beloved’ (cf. OHG liub, liup, OSax liof).
I’ve two additions. First, I suggest Liebizo as the best normalized form of the name: it’s the one that seems to be most widely used. Secondly, I’ve an example of a very closely related name. The Latinized genitive Liubisi 863 from Fulda probably represents Liubiso, with a similar (and perhaps earlier) suffix.
I think this one is rather straightforward: It is an -izo diminutive of a name containing the theme liab (High German) / liaw (Low German), cognate to modern High German lieb “dear; nice; beloved”. At the time of the recording of the name, liab still contained a falling diphthong like ia that is preserved upto today in the Bavarian dialect.
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