means A weight suspended from a fixed point so it can swing freely back and forth under gravity, used to keep time or to demonstrate motion.

from From the Latin 'pendulus,' meaning 'hanging,' which traces back to the verb 'pendere,' 'to hang' — the same root that dangles inside 'pendant,' 'suspend,' and 'pending.' The modern scientific sense was coined in the 17th century alongside the realization that a swinging weight keeps remarkably steady time.