The personal names Tigernach or Tighearnach (Tierney) and Tigernan or Tighearnan (Tiernan), and the surnames Ua Tigheranaigh (O'Tierney), Ua Tighearnain (O'Tiernan) or Mac Tighearnain (McTiernan), come from the Gaelic word Tighearna, from the same Indo-European root source as the Greek "Turannos" and Latin "Tyrannus".

The word originally meant king, and is now generally translated in Gaelic and Irish dictionaries as lord.

The Gaelic "Tir na" means "land of" and in early Celtic tales it was believed that there was a connection between the land and its ruler.

The land prospered under a good ruler, and was barren under a bad ruler. The tales of King Arthur and his court carry this symbolism into mainstream western literature.

In Gaelic records the various clann chieftains and rulers are referred to by the title tighearna.