Definition of sima in English:

sima

noun

Geology
dated
  • [mass noun] The material of the lower part of the earth's crust, underlying both the ocean and the continents, characterized as relatively heavy and rich in silica and magnesia.

    Contrasted with sial
    • ‘The sial and sima both form the earth's crust which varies in thickness.’

Origin

Early 20th century: blend of silica + magnesium.

Pronunciation:

sima

/ˈsʌɪmə/