Above is the coat of arms of the Ó Tighearnaigh family (anglicized to Tierney). According to Irish Families: Their Names, Arms & Origins by Edward MacLysaght (1957), this coat of arms has a long history. It was confirmed in 1748 to a County Limerick branch of the Tierney family. The patent of that date for the coat of arms states that the family was a "long user thereof".
The name Tierney originated from the Gaelic word tighearna, meaning "lord". Different branches of the Tierney family appear to be quite widespread throughout Ireland, although it is most common in Galway, Limerick and Tipperary, where our branch of the family lived.
In fact, the Ó Tighearnaighs, according to MacLysaght, were "undoubtedly firmly established as a territorial family, if not an indigenous sept, in Upper Ormond, for in the Ormond Deeds Fearnan O'Tyernie (i.e. O'Tierney's country) is several times mentioned." See more information on the records in the Ormond Deeds at the Tierney Clan Society webpage on the subject.
Ó Tighearnaigh - the name looks so much prettier written in Gaelic, don't you think? I've always been pretty good at spelling, but these Gaelic spellings are a bit more challenging. If I'm serious about researching my family's Irish history, I'll have to dedicate more time to working on my Gaelic...
(Note: the current edition of MacLysaght's book is pictured above. The link to purchase the book is on the Related Reading sidebar.)