thumbhole
/ˈθʌmbhoʊl/Definitions
1. noun
A hole at the end of a guitar neck, typically to adjust the pitch or to facilitate playing with the thumb.
“The musician adjusted the guitar’s thumbhole to get the perfect sound.”
2. noun
A small hole or opening in a solid object, especially for a finger or thumb to fit through.
“The designer created a thumbhole in the wooden door to make it easier to open.”