English▸ noun hot fluid or semifluid material below or within the earth's crust from which lava and other igneous rock is formed on cooling:
when red-hot magma comes into contact with seawater, an explosion results
[count noun] basaltic magmas are normally expelled at the surface in a very hot and fluid state.
– ORIGIN late Middle English (in the sense ‘residue of dregs after evaporation or pressing of a semiliquid substance’): via Latin from Greek magma (from massein ‘knead’).