How do you say sheahan in Irish?

There isn't a direct equivalent of the surname Sheahan in Irish. It's an anglicised surname, and its origin and therefore its Irish equivalent would depend on the original Irish form. It's likely derived from a few possibilities, including:

* Ó Séagháin: This is a possible origin, meaning "descendant of Séaghán." Séaghán is a personal name.

* Variations: There could be other variations depending on the specific pronunciation and spelling of the original Irish form.

To find the most accurate Irish equivalent, you would need more information about the family's origins and the spelling variations used in the past. Genealogical research might be necessary.