Nicknames:
Tier.
Famous people named Tiernan:
Ancient Irish king Tiernan O'Rourke; comedian Tommy Tiernan.
Fun fact:
The similar name Tierney is also derived from the same root name.
More Inspiration:
If You Like Liam, You’ll Love …, Álainn! Irish Baby Names, Terrific Two-Syllable Girl Names, Terrific Two-Syllable Boy Names, Unisex Names Perfect For Any Gender,