What are the etymological roots of the Italian family name “Cusamano” and the Spanish name “Guzman”?
They seem alike enough that I wondered if they were versions of the same name in different languages.
Both are from the Arabic name Quzmân. There was a Spanish Arab poet named Ibn Quzman (c.1080-1160). Here is his charming little poem, “The Radish.”
*The radish is a good
And doubtless wholesome food
But proves, to vex the eater,
A powerful repeater.
This only fault I find:
What should be left behind
Comes issuing instead
Right from the eater’s head!*
The name Quzmân is an unusual one in Arabic; it seems to be related to the word qazam meaning ‘midget, pymgy, Lilliputian, hop-o’-my-thumb’, etc. Maybe it originated as a satirical deformation of the well-known Arabic name ‘Uthmân. Just a guess. The poet Ibn Quzmân was a popular showman and minstrel in 12th-century Córdoba.
Wow, thanks for the reply! I had given up hope on this question.
Wow. You are really frickin’ smart!
That’s so sweet of you. 
I just got the mental image of Ibn Quzman reciting this poem in a public performance, and punctuating it with an enormous belch. Always a crowd pleaser.
What a great answer, can you tell us your sources? How did you learn about this?
I first discovered Ibn Quzman over 20 years ago, when I got the old Anthology of Islamic Literature, edited by James Kritzek, for one buck in a used bookstore (Mac’s Backs on Coventry in Cleveland Heights, Ohio… I don’t know if the store is still there or not). I got into the unfortunate habit of reciting that poem whenever radishes were served.
I looked up the meaning of the Arabic root Q-Z-M in the Dictionary of Modern Written Arabic by Hans Wehr. I was familiar enough with the Maghribi (North African) dialect of Arabic that I could recognize the sound shift from Q > G. I once dated a Chicana theological student named Luz Guzmán. She it was who first told me about process theology. She was getting ready to go to Nicaragua as part of the Witness for Peace program. This was in 1984 when Reagan was making war on the Nicaraguan people. She was very brave.
I found a bio of Ibn Quzman on the Aramco World magazine web site.
Just got round to reading this thread. ‘Guzman’ could well be Arabic in origin, as are many Spanish surnames. The most famous historical Guzman ‘El Bueno’ is noted for having fought the Moors, so if he himself was of Arab origin he had left that legacy far behind. (BTW The link referenced provides yet another explanation for the origins of the family name.)
The mainstream theory - at least according to the more popular Spanish genealogy sources - is that it came from the Visigoth invaders. Gutman?
Don’t know of any connection to the Italian name, but it is certainly related to the Portuguese ‘Gusmao’.
Hmm… the Gothc word for good is goda. I’m not sure how you would get from goda to Guz-, or how plausible it is. Maybe from Gothic Guþ ‘God’? The Gothic letter þ was pronounced similar to Spanish z. I tried the Wörterbuch der gotischen Namen but didn’t find anything that looked like Guzmán. Are you sure it wasn’t just a case of Spaniards preferring Germanic ancestry over Arab ancestry?
Guþman sounds almost exactly like the Arabic name ‘Uthmân, except for the initial letter. However, in Azerbaijani and Tatar, the letter G replaces the Arabic letter ‘ayn (the initial letter of ‘Uthman). I’m not saying this explains it, just noting an odd coincidence.
Spaniards don’t play down their country’s Arab heritage, at least not in my experience. This legacy is more often than not celebrated in Spanish culture, and acknowledged as the source of many words in the Spanish language and the origin of many common surnames and place names. (Anything beginning with ‘Al’ or ‘Guada’ for a start).
The other common theory is not so much that Guzman derives from ‘Gutman’ but from ‘Gundamaris’.
Brits then? The plot thickens. 
I agree though that the similarity to ‘Uthman’ makes for a more convincing explanation.
Forgot to respond to this bit - G replaces 'ayn in non-Arabic renditions of Arabic words or names, not just in the places you mention: Gaza for instance. Can’t think of any other examples at the moment. It certainly adds credence to the theory.
The first letter of Gaza in Arabic is ghayn, not ‘ayn. They’re written the same, except that ghayn has a dot over it. They’re not pronounced similarly, though.