thirdpiece
nounUK /ˈθɜːd.piːs/
US /ˈθɝːd.piːs/
The third piece is the one that comes after the first two.
She ate two cookies and saved the thirdpiece for later.
OTHER MEANINGS
2. A third separate component that completes a set of three.
The puzzle was missing its thirdpiece, so the picture stayed incomplete.
3. The third share of something that has been split into three parts.
Each child got a thirdpiece of the cake.
4. A third musical or artistic work in a series.
The band released the thirdpiece of their trilogy last spring.