magma

Concise Oxford English Dictionary © 2008 Oxford University Press:
magma /ˈmagmə/

▶noun (pl. magmas or magmata /-mətə/) hot fluid or semi-fluid material within the earth's crust from which lava and other igneous rock is formed by cooling.

– derivatives
magmatic adjective.

– origin ME (in the sense ‘residue left after evaporation or pressing of a semi-liquid substance’): via L. from Gk magma (from massein ‘knead’).