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 found in early 16th C Italy, in a taxation record for one “Faustina cortesana in casa di madona Iesmonda”:
It’s a particularly vexing name, because for more than a year now there has been some clue about its origin hovering just outside of ready access memory, and no matter how ingenious we’ve been in our searching, we just can’t figure it out. So we’re tapping in to the collective knowledge of the internet: What is the very-similar-but-not-quite identical word that we haven’t been able to think of that is the likely candidate for this name’s origin? If you know, or have a thought, please share in the comments!
Dictionary of Medieval Names from European Sources 
In Galicia and NW Iberia:
“Gismundus abbas”, 921, Sahagún
“Gesmundo”, 937, Galicia
“Gismondu Sonegeldi”, 949, Portugalliae Monumenta Historica
“Gesmondo”, 996, Galicia
East Germanic? From *gaizaz?
There is one other “Jesmonda” in 1560 (“Il libro delli battizzati dell’anno 1537”, p. 194). My guess is that it’s a variation of “Gismonda”; cfr. “Hismonda” from 1609 (“Il predicatore di F. Francesco Panig”, p. 629, referring to Ghismonda, a character in Boccaccio’s Decamerone); and “Gesmonda” from 1504 (Rerum Italicarum Scriptores 15.5.2, p. 252). There are two “Gismonda” in the same census LeoX. If this is correct, the origin could be just the same as “Gismunda” which you already have in the dictionary.
My first association is a geographical name: Jasmund, a paeninsula and part of the German Island Rügen in the Baltic sea. This association might provide a clue, because Jasmund is derived from a personan name, according to Ernst Eichler, Onomastica Rugiana. Plädoyer für die Toponymie einer Insel, in: Namenwelten: Orts- und Personennamen in historischer Sicht (Berlin 2004), S. 37 (cited after the German Wikipedia entry on Jasmund):
I found a number of Italian instances of Ges(i)monda, which is surely a feminine form of the Germanic name seen in Latinized Ostrogothic Gesimundus; here the prototheme is PGmc. *gaiza- ‘spear, javelin’, and the deuterotheme is PGmc. *-mundō ‘protection, security’. I suspect that Iesmonda is a variant of this; cf. Ieswaldo, a variant of Gesualdo, with the same prototheme, and note that lenition of [g] to [j] before a front vowel is not uncommon.
I would’ve suspected it might be a variant of the Decameron name Ghismonda, because Bocaccio was an Italian writer and the work came out in the 1300’s. However, Withycombe’s Oxford Dictionary of English Christian Names says Jesmond is related to Ismenia.
Oooh, yes, that seems quite likely!
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