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Re: british and other countries surnames: Cassin- Casson
Casson, English, and according to Reaney's surname dictionary, can mean "son of Catt" (Catherine?), or "son of Cass", short for Cassandra, so a metronym.
Cassin is both Irish and Manx, i.e., Gaelic; MacCaisin originally, "son of Caisin" a man's name which incorporates the word cas, crooked."
There's also a French surname Cassin, presumably from a place-name. It derives from an old Celtic word for an oak tree, as do the Italian names, Cassano and Cassani.
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I'd just add, that the Irish name Cassidy is looks to also be related and the term crooked has been said to mean "curly" and in curly hair ...
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I Never thought of that possibility. Some old Irish personal names seem uncomplimentary, and you wonder why they were bestowed on chidren.
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You may find some historical interest in the surname of my mother, that reveals an early 'Cas'

http://www.sjfoley.com/Meaning_of_McCarthy_Name/McCarthy_Name.htm
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