mantle
n. countablen. the layer of rock inside a planet between the outer crust and the hot center. It can also mean a role or responsibility that passes from one person to another.
n. the layer of a planet between the crust and the core, composed of silicate rocks; also used metaphorically to refer to a position of authority or responsibility passed between individuals.
The Earth's mantle is made of hot, solid rock.
After the CEO retired, the young director took up the mantle of leadership and began modernizing the company.
Geologists study how heat moves through the mantle to understand the shifting of tectonic plates, while historians often describe how the mantle of power was handed down through royal dynasties.
Often used in the figurative phrase 'take up the mantle' or 'pass the mantle', followed by the preposition 'of'.