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 from 12th C France, and was one that, before we wrote this post, was utterly opaque to us:
Researching it for this post, though, led us to two more examples. One is a woman named “Barisia, cognomento Ginnosa”, wife of Rainald cognomento Barbatus, who gave money to a monastery in 1139, and another is a Gignosa, one of three daughters of Petrus Simonis (the entire family has lovely names; his wife is Helisabeth, Gignosa’s sisters are Laurentia and Aldeburgis, and their brother is Aimericus), who made a donation around 1120.
Two other relevant pieces of information that we turned up: First is the Greek word ιννος or γιννος ‘mule’, found in Chambers’s Etymological Dictionary of the English Language. The other is the occurrence of the word ginnosa in 13th-century Provencal literature, in the Romance of Flamenca, and in the Cort D’Amor. So! Do we have any southern French scholars amongst our readers? Do you recognise this word? Know what it means? Know what its root might be? Please share in the comments!
Dictionary of Medieval Names from European Sources 
Given the names of some relatives, a Germanic interpretation of the Ginnosa is maybe also possible.
Förstemann (1900) has a stem GIN that he tentatively links with Old Norse ginna “to seduce; to attract; to lure” but the stem cannot be clearly separated from the stems GAN (related to magic or miracle) and GEN (related to birth, compare Celtic and Greek genos).
There is also the Old High German word ginoz “comrade, partner, mate” (Modern German Genosse) listed as a name in Förstemann (1900).
So it can be either a diminutive if Ginna (monothematic name from the stem GIN) with an Italian-style diminutive ending to a Germanic stem, or a feminine form of ginoz.
This source glosses Provençal ginnosa as adroit, ingénieux and this one as ‘rusé, habile, malicieux’, on the face of it a very plausible byname. In the Martyrologe de l’insigne collégiale Notre-Dame de Beaune it appears as a masculine byname in the entry for the death of Bella, uxor Guidonis Ginnosa, XII Kal. Aug., 1270.
I suspect that the word is an aphaeretic derivative of a Provençal cognate of Old French engignos ‘habile, adroit, avisé’.