Sean is an Irish Language name. It is Irish borrowing of the Norman French Jean. Anglicisations of the name comprise Sean, Shane, Shayne, Shan, Shon, Shaine and Shawn. The name Shane comes from the Ulster pronunciation of the name, while the names Shaun, Shawn or Sean come from the way it is prominent in Munster, Leinster and Connacht.
In 1066, the Norman duke, William the Conqueror overpowered England, where the Norman French name Jehan/Johan came to be.
In 1066, the Norman duke, William the Conqueror conquered England, where the Norman French name Jehan / Johan (pronounced [dʒɛˈan]) came to be pronounced Jean, and spelled John. The Norman from the Welsh Marches, with the Norman King of England's mandate conquered Ireland in the 1170s. The Irish nobility was put back by Norman nobles, some of whom bore the Norman French name Johan or the Anglicised name John. The Irish adapted the name to their own pronunciation and spelling, producing the name Seán.
Sean is usually pronounced Shawn (Seán), but in the northern parts of Ireland, it is said "Shan", "Shen" or "Shayn", thus leading to the variant Shane.