Meaning: It may be related to Old Irish sen meaning “old, ancient” and abhainn meaning “river”. I’ve also seen it listed as meaning “wise”.
It’s also the Anglicization of Gaelic surname Ó Seanáin meaning “descendant of Seanán”, the latter meaning “old”. It could also be related to O’Sionain, referring to someone who worked with straw.
As well as also being the name of the longest river in Ireland, Shannon is also associated with the Irish goddess Sionna