cruisefortibet's list "Boy names" of 3 great name ideas: Kiernan - Tiernan!

Boy names

Although this surname name is closely related to the more common Irish name Kieran, Kiernan is also a well used family name, tied to thirty-three ancient chieftains. It has on a few occasions been used for girls.

Kiernan

If you like the idea of Tadhg but don't feel like the spelling works where you are, Teague might work as an alternative. It could also fit the bill if you're seeking a unique single-syllable first or middle name for your son. 

Teague

Tiernan is the slightly edgier and sharper cousin of Kiernan. This is one Irish surname that is attractive but distinctive; Tierney is another, related, option.  
<br/><br/>Tiernan was a popular name in early and medieval Ireland and was borne by several kings and saints.  It is currently high on the list in Northern Ireland.