12 letters · 24 points in Scrabble
noun an instrument that indicates whether two periodic motions are synchronous (especially an instrument that enables a pilot to synchronize the propellers of a plane that has two or more engines)
originFrom synchro- + -scope, from syn- + chrono- + -scope, from Ancient Greek σύν (sún)+χρόνος (khrónos)+σκοπέω (skopéō).
Etymology from Wiktionary, CC BY-SA 3.0