mid-15c., "dregs," from Latin magma "dregs of an ointment," from Greek magma "thick unguent, ointment," from root of massein "to knead, mold," from PIE *mag- "to knead" (see macerate). Geological meaning "molten rock" is 1859. Related: Magmalic.
magma mag·ma (māg'mə)
n.
A mixture of finely divided solids with enough liquid to produce a pasty mass.
A suspension of particles in a liquid, such as milk of magnesia.
Molten rock usually located deep within the mantle of the Earth that occasionally comes to the surface through cracks in the mantle or through the eruption of volcanoes.
Note: When magma cools and solidifies, it forms igneous rock, of which lava is one type.