keypiece
nounUK /ˈkiːpiːs/
US /ˈkiːpiːs/
A keypiece is the most important part that holds everything else together.
The big stone in the middle of the arch is the keypiece that keeps it from falling down.
RELATED WORDS
OTHER MEANINGS
2. The central piece in a puzzle or game that everything else fits around.
She found the keypiece of the puzzle first, and the rest was easy.
3. A crucial element in a plan or story that makes the whole thing work.
That clue was the keypiece of the mystery.
4. A small but essential part of a machine or device.
The tiny gear is the keypiece that makes the clock tick.