Definitions

1. noun

A person born third in a family, often used to describe a member of a family that has two older siblings.

“Growing up as a thirdling in a family of five was a unique experience.”

2. noun

In J.R.R. Tolkien’s Middle-earth legendarium, a thirdling is a member of the Dwarves of the Blue Mountains.

“The thirdlings were known for their skill in mining and craftsmanship.”