Moho
noun
Mo·ho ˈmō-ˌhō 
: the boundary layer between the earth's crust and mantle whose depth varies from about 3 miles (5 kilometers) beneath the ocean floor to about 25 miles (40 kilometers) beneath the continents
Word History
Etymology
short for Mohorovicic discontinuity, from Andrija Mohorovičić †1936 Yugoslavian geologist
First Known Use
1952, in the meaning defined above