Finnian

The name Finnian was given to 164 boys born in the US in 2015.

This is an awesome, strong name, but I can guess why it isn't very popular. It's dangerously similar to the vicious sectarian slur "Fenian" which is used in Northern Ireland and Scotland against Roman Catholics. The word itself comes from the Irish fianna, the name of a band of mythical warriors in Irish mythology. The name was anglicised "Fenian" and used by the Fenian Brotherhood and Irish Republican Brotherhood as a name for their members. They were later called more political terms like "Nationalist" or "Republican", but nowadays, "Fenian" is used as a very taboo insult for Catholics in general, equivalent to the n- word.